FR2582966A1 - Process for milling granular materials and means for implementing the process - Google Patents

Abstract

The invention relates to a process for milling granular materials, such as clinker or coal for example. The process uses a mill 1 comprising at least one cylindrical tube 2 with at least one compartment 9, 10, 11. It is characterised in that the quantity of milling bodies of each size is determined for at least one of the compartments 9, 10, 11 so that their overall useful surface follows a homothetic progression, whose transformation rule is determined from physical and/or chemical parameters characteristic of the material to be milled and of data specific to the mill. The invention also relates to means for implementing the process. Application to milling.

Description

 The invention relates to a process for grinding granular materials, as well as to means for implementing the process.

 In particular, but not exclusively, the invention relates to the grinding of granular materials such as, for example, clinker or coal.

 It is currently known to grind such materials by using at least one cylindrical tube, which has on one side an inlet orifice for the ground materials, and on the other an outlet orifice and which is driven rotating around its generally horizontal axis.

 The cylindrical tube has one or more compartments.

 Each compartment is filled with grinding bodies which are in particular constituted by spherical balls or elements known by the name of Ucylpebs, that is to say cylindrical elements whose height is substantially equal to the diameter.

 The crusher is filled with different sizes of grinding bodies, so as to gradually reduce the length of the material to be ground, the largest sizes being on the inlet side, and the finest on the side of the material outlet. grind, and each compartment contains several sizes of grinding bodies for this purpose.

 We know how to determine the maximum volume of grinding bodies that a compartment can contain by a calculation involving the geometric dimensions, those of the inlet orifice and the outlet orifice, of the orifices of the partition walls of two successive compartments.

 On the other hand, for each compartment, the quantities of grinding bodies of each size are most often determined empirically, from a distribution of weights or a distribution of numbers most often based on use.

 Sometimes, the C2S module of the material to be ground intervenes for the determination of the relative quantities of the balls of different calibers but without real efficiency.

 The methods currently known for determining these quantities of balls of different sizes therefore do not give the best results in terms of grinding of granular materials because their main defect is that they do not take sufficient account of the physical characteristics of the material to be ground and, therefore, , the load of a mill is rarely optimal for a defined material.

 In addition, the methods currently used do not make it possible to control the course of the grinding and in particular, they do not make it possible to effectively correct the distribution of the grinding bodies of the different sizes * in particular in the case where clearly the efficiency of the grinder is not optimum.

 One of the aims of the present invention is to propose a grinding process and means for implementing the process, which makes it possible to optimize the distribution of the loads of grinding bodies in the different compartments of a grinder, taking account of the material. granular to be ground.

 Another object of the present invention is to provide a method and means for controlling the adaptation of the load of grinding bodies to the material to be ground and for correcting it if necessary.

 Another object of the invention is to propose a method and means which can be easily adapted to any existing type of mill.

 Other objects and advantages of the present invention will become apparent from the following description.

 The grinding process of the invention uses a grinder consisting of at least one cylindrical tube which rotates around its axis, with an inlet port on one side and an outlet port for the materials on the other to be ground * and each tube includes at least one compartment.

 Each compartment is partially filled with a defined volume of grinding bodies of different sizes, each size comprising grinding bodies having substantially the same main dimension, in particular an average diameter.

The process is characterized in that:
- a theoretical result is calculated for all of the compartments from at least two physical and / or chemical quantities characteristic of the material to be ground,
- for at least one of the compartments, a correction coefficient is applied to said resultant and a corrected resultant is calculated,
- the said compartment is loaded with different sizes of grinding bodies, the quantity of which is determined so that the overall useful surface of the grinding bodies of each size responds to a homothetic progression whose season of homothetic evolution is determined according to the said corrected result , the sizes of grinding bodies being considered in the order defined by the main dimension of the grinding bodies which belong to them respectively.

 The means for implementing the method are characterized in that they comprise, for all of the compartments, means for calculating the theoretical result, for at least one of the compartments, means for calculating the correct result and overall useful surfaces for each size of grinding bodies, from physical and fou chemical quantities representative of the material to be ground and the neometric dimensions of said chamber of the mill.

The invention will be better understood by referring to the description below, given by way of nonlimiting example, with reference to the appended drawing which schematically represents
- Figure 1: a cross-sectional view showing a mill comprising three compartments,
- Figures 2 and 3: two curves representing the distribution of the grinding bodies on the one hand, of the material to be ground, on the other hand, over the length of the mill and illustrating the control of the load of the mill.

 In order to facilitate its understanding, the invention will be described in the application to a clinker mill, comprising a cylindrical tube and three compartments.

 This application is not limiting and the invention also applies to any mill intended for other materials, in particular coal, and generally to any type of mill, comprising any number of cylindrical tubes, of compartments.

 In the illustration for non-limiting application to a clinker mill mentioned above, FIG. 1 represents a mill 1 constituted by a cylindrical tube 2, driven in rotation about its horizontal axis 3.

 The cylindrical tube 2 comprises on one side an inlet orifice 4 for the material to be ground, and on the other an outlet orifice 5 for the ground material with in particular a forced ventilation to propel the material to be ground from the inlet to the mill outlet.

 Depending on the types of installation, the crusher 1 operates in an open circuit or in a closed circuit, that is to say in the latter case that the ground material at the outlet passes through a separator which recycles the underground ground grains towards the inlet 4.

 The crusher 1 shown in Figure 1 has three compartments 9, 10, 11 separated by partitions 8, 12 single or double of a known type.

 Each compartment 9, 10, 11 is partially filled with a defined volume of grinding bodies, respectively represented at 13, 14, 15.

 For each compartment 9 to 11, the volumes 13 to 15 of grinding bodies consist of grinding bodies of different sizes.

 The sizes of the grinding bodies are defined in particular by one of their main dimensions, this can be in particular the diameter for spherical balls, and also the diameter for elements known as "cylpebs", which are cylindrical elements of which the diameter is equal to the length or sometimes whose length is twice the diameter.

 By way of nonlimiting example, it will be assumed that the volume 13 of grinding bodies of the first compartment 9, is constituted by balls of caliber 90 millimeters, 80 millimeters 70 millimeters and 60 millimeters that the second compartment 10 mainly contains balls of calibers 50 millimeters, 40 millimeters and balls of caliber 60 millimeters and that the third compartment 11 contains balls of caliber 30 millimeters, 25 millimeters, 20 millimeters, 17 millimeters.

 Naturally, this is only an example given by way of illustration and the volumes 13, 14, 15 of grinding bodies could be constituted by any other distribution of sizes and any other type of body.

 The internal wall of each compartment 9 to 11 is optionally coated with any suitable means, for example classifying shields, shown diagrammatically at 16 for the compartments 10, 11 so that during the rotation of the crusher, inside each chamber, the crushing bodies classify themselves according to decreasing ratings, from the entry to the exit of the compartment.

 In certain cases, the use of classifying shields means that the crusher only has a partition 8 between the first compartment and the next, and the separation between the second and the third compartment is in this case fictitious.

 The crusher 1 is driven in rotation around its axis 3 by any suitable means, and the angular speed of rotation is usually of the order of 75% of the critical speed, that is to say the speed at which, under the effect of centrifugal force, the grinding bodies remain stuck to the wall of their compartment.

 According to the process of the invention, a theoretical result is first calculated, defined by at least two physical and / or chemical quantities characteristic of the product to be ground.

 For clinker, the theoretical result is a linear relation involving at least two of the following quantities, KUHL module (mK), C2S module (C2S), silicic module (mis), alumino-ferric module (maf), clinker density , which are quantities commonly used to define the physical and / or chemical characteristics of the clinker to be ground.

The theoretical result R can be calculated by the following formula
R = Ax mK - Bx C2S - Cx mS - Dx maf + E
4 where A, B, C, D and E are constants.

By way of illustration, good results have been obtained by taking the following values:
- Between 2.25 and 2.75
- B between 0.0045 and 0.0055
- C between 0.18 and 0.22
- D between 0.23 and 0.27
- E between 2.4 and 3.0
- the various modules evaluated according to international standards of the "SEMBUREAU".

 Naturally, these figures are only indicative with regard to the invention.

 It should be noted that the theoretical resultant R is representative of the material to be ground and therefore that it is generally calculated for all the compartments.

 From the theoretical result R, a corrected result Rc is determined, for at least one of the compartments, by applying one or more multiplicative corrective coefficients to the theoretical result R.

 For the different compartments, the correction coefficients depend on the position of the compartment considered within the mill.

 They also depend on the open circuit or closed circuit operating mode of the mill.

By way of nonlimiting example, good results have been obtained for a grinder such as that shown in FIG. 1, operating in an open circuit with the following correcting coefficients, for the different compartments:
- 0.10 for the first compartment 9,
- 0.20 for the second compartment 10,
- 0.15 for the third compartment 11.

For a similar mill operating in a closed circuit, good results have been obtained with the following correction coefficients:
- 0.20 for the first compartment 9,
- 0.30 for the second compartment 10,
- 0.10 for the third compartment 11.

 Naturally, these figures have no limiting value for the invention.

 A multiplicative corrective coefficient is also applied to the resultant, which is determined after a certain time of operation of the mill, on the basis of the control of the particle size of the material to be ground along the mill.

Initially, this correction coefficient is equal to unity and it is adjusted during the operation of the mill following the checks carried out
Using the corrected resultant RC, for the compartment considered, the quantity of grinding bodies of each caliber is determined, so that the overall useful surface of the grinding bodies of each caliber corresponds to a homothetic progression relationship that is ie geometric progression whose reason for evolution is determined from the corrected resultant.

 The overall useful surface is the total external surface of the grinding bodies of the same size.

 The grinding body sizes are considered for each compartment in the order defined by the main size of their grinding bodies and, preferably, they are considered in decreasing order, from the highest size to the lowest size.

 Given this sense, the reason for the evolution of the homothetic progression which determines the overall useful surface of each size of grinding bodies is equal to the corrected result increased by unity.

Considering the previous application example, for the grinding of clinker having the following characteristics
- KUHL module: mK = 0.93
- C2S module: C2S = 25.00
- silicic module: mS = 2.15
- aluminum-ferric module: maf = 1.50, the mill operating in open circuit, the theoretical result has a value of about 1.025, the corrected result has a value:
- Rc = 0.1025 for the first compartment 9,
- R'C = 0.2050 for the second compartment 10,
- R "C = 0.1538 for the third compartment 11.

The reason for the evolution of the homothetic progression determining the overall useful surface of each size of grinding bodies is as follows
- 1.1025 for the first compartment 9,
- 1.2050 for the second compartment 10,
- 1.1538 for the third compartment 11.

 For a defined compartment, from the useful filling volume, i.e. volumes 13 to 15, and taking into account the relationship which links the overall useful surfaces of each size of grinding media, it is possible to calculate the quantity or tonnage of grinding media of each caliber.

By way of nonlimiting example, for the first compartment 9, it is possible to operate in the following manner
- chamber volume: 53.66 m3,
- filling rate selected: 0.295
- one useful theft: 53.66 x 0.295 = 18.78 m3,
- total tonnage: (usable volume x average density): 18.78 x 4.55 = 85.45 tonnes.

 A density of 4.55 T / m3 is the value generally adopted for spherical balls.

The load distribution coefficient C is then calculated according to the following formula
C = 1 + (80 / 9Q) x (-1 + Rc) + (70/90) x (1 - + RC) + (60/90) x (1 + Rc) 3 with RC = 0.1025 d ' where C = 3.82
The tonnages of the balls of different calibers are obtained as follows
- 90 ball: T90 = Tt / C = 22.38 tonnes
- 80 ball: T80 = Tt / Cx (80 / 90-) x (l + RC) = 21.93 tonnes
- 70 ball: T70 = Tt / Cx (70/90) x (1 + RC) = 21.16 tonnes
- 60 ball: T60 = Tt / Cx (60/90) x (l + RC) = 19.99 tonnes
Knowing the tonnage of each caliber of ball, it is easy to deduce the number of balls.

 For the second compartment 10 and the third compartment 11, the determination of the quantities of balls of each caliber is slightly different.

 As before, the useful volume of the compartments is defined, but in addition a tonnage distribution ratio is defined between the two compartments 10, 11 which depends on the nature of the balls and on the position of the partition 12 and which is generally understood. between 0.2 and 0.3.

By way of example, the determination can be made as follows
- total volume of the second compartment and the third compartment: 120.9 m3
- filling rate selected: 0.310
- useful volume: 37.49 m3
- total tonnage: 178.06 tonnes
- tonnage distribution ratio between the two compartments 10, 11: 0.28
second chamber tonnage: Tt '= 49.86 tonnes
- third chamber tonnage: Tt "= 128.20 tonnes
The second compartment 10 contains 50 millimeter and 40 millimeter caliber balls whose overall specific surface is connected by a relationship of geometric progression.

 However, given the presence of the partition 8 with the first compartment 6, a tonnage of 60 mm caliber balls is added which represents one fifth of the overall tonnage of the first chamber of the second compartment, that is to say in the present case: T60 = 9.97 tonnes, to ensure continuity between the first and second compartments.

 The third compartment 11 contains balls of caliber 30, 25, 20 and 17.

The determination of the tonnages of each caliber is done in the same way as in the previous case, taking into account the homothetic progression which links the overall useful surfaces of each category of grinding bodies, with the reasons for the following progression
- 1.2050 for the second compartment 10,
- 1.1538 for the third compartment 11.

So the second compartment 10
- load distribution coefficient C '= 1 + (40/50) x (1 + RC') = 1.964 with RC '= 0.2050, hence the following tonnages of grinding media of each caliber:
- 50 ball: T50 '= (Tt' - T60,) / C '= 20.31 tonnes
- 40 ball: T40, = T50'x (40/50) x (1 + Rc 19.58 tonnes
For the third compartment 11
- load distribution coefficient
C '' = 1+ (25/30) x (1 + Rc '') + (20/30) x (1 + Rc '') 2+ (17/30) x (1 + Rc '') 3 = 3.72 T with Rç "= 0.1538 hence the following tonnages of grinding media of each caliber
- 30 T30 "ball = Tt" / C "= 34.47 tonnes
- ball of 25 :: T25 "= Tt" / C "x (25/30) x (1 + RC") = 33.14 T
- ball of 20: T20 "= Tt" / C "x (20/30) x (l + Rç") 2 = 30.59 T
- ball of 17: T17 ,, = Tt "/ C" x (17/30) x (l + Rc ") 3 = 30.00 T
Naturally, it goes without saying that all of these figures have only an illustrative value for the invention and have no limiting value, in fact, they depend on the material to be ground and both the grinding plant itself.

 Those skilled in the art are able to determine the chain of means ensuring the functions of the different stages of the process and which make it possible to calculate, as a function of the specific data of the material to be ground and of the grinder, the quantities of the different sizes of grinding bodies to be loaded in the different chambers of the mill.

 In a preferential mode, these means will be computer means.

 According to the invention, after loading the mill, the adaptation of the load of each chamber to the material to be ground is checked during operation.

 To do this, the mill is stopped at full load and samples are taken at regular intervals along the length of the mill.

 The particle size of the material to be sampled is for example evaluated by measuring, for a sample mass give the amount of material to be ground refusing passage through the grid of a sieve of determined size, for example two hundred microns.

 The curve representative of the particle size of the material to be ground, along the grinder, is shown by way of illustration in FIG. 3.

 According to the invention, a curve is also established which represents on the ordinate the logarithm of the diameter of the grinding bodies or of their size, according to their position along the length of the grinder.

 Such a curve is shown by way of illustration in FIG. 2.

 The control of the adaptation of the load of the mill to the material to be ground is done by comparing the shape of these two curves, the variations of which must follow each other substantially or more exactly by checking whether the grain size curve in FIG. 3 generally follows the same variations as the rating curve in Figure 2.

 If the two curves do not correspond or, for example the curve in Figure 3 has a clear angular point on the length of one of the compartments, it is possible to apply a control correction coefficient on the theoretical result, and to determine a new corrected result and a new distribution of the grinding bodies of different sizes inside the different compartments of the grinder.

 The origin of an anomaly observed on the granulometry curve of the material to be ground, can also come from a bad ventilation inside the mill or from an excessive permeability of the grinding bodies.

Naturally, the present description is given for information only and other implementations of the invention could be adopted without departing from the scope thereof.
In particular, for a coal mill, the determination of the amounts of grinding bodies of each category would be done in a manner similar to what has been described in the application to the clinker mill.

 The characteristic physical quantities of the material to be ground are however different and in the case of coal, it is in particular the percentage of volatile matter, the percentage of ash, the average hardness of the coal, and its average humidity.

Claims (1)

CLAIMS Process for grinding a granular material such as for example clinker, carbon, using at least one cylindrical tube (2) driven in rotation around its axis (3) with an inlet opening on one side (4) and on the other an outlet (5) for the material to be ground, each tube (2) having at least one compartment (9, 10, 11), each compartment being partially filled with a defined volume ( 13, 14, 15) of grinding bodies of different sizes, each size comprising grinding bodies having substantially the same main dimension, in particular an average diameter, CHARACTERIZED by the fact that - all the compartments are calculated (9, 10,  11) a theoretical result (R) from at least two physical and / or chemical quantities characteristic of the material to be ground,  - for at least one of the compartments (9, 10, 11), a correcting coefficient is applied to the said theoretical resultant (R) and a corrected resultant (RC) is calculated,  - said compartment (9, 10, 11) is loaded with different sizes of grinding bodies, the quantity of which is determined so that the overall useful surface of the grinding bodies of each size responds to a geometric progression whose evolution reason is defined at from the said corrected resultant (RC), the sizes of grinding bodies being considered in the order defined by the main dimension of the grinding bodies which constitute them respectively.  2. Method according to claim 1 characterized in that one determines for each compartment (9, 10, 11) the amount of grinding bodies of each caliber so that the overall useful surface of the bodies. grinders of the different calibers taken in decreasing order of the main dimension, responds to a relationship of geometric progression whose reason for evolution is the so-called corrected result (Rc) increased by unity.  3. Method according to claim 1 or 2 characterized in that for each compartment (9, 10, 11) is applied a correction coefficient defined by the position of the compartment (9, 10, 11) within the crusher (1).  4. Method according to claim 1 or 2 characterized in that for each compartment (9, 10, 11), a corrective coefficient is applied depending on the operating mode open circuit / closed circuit of the crusher (1).  5. Method according to any one of claims 1 to 4 applies to a clinker mill, characterized in that one determines the said theoretical result (R) for all of the chambers (9, 10, 11) to from the following linear relation R = A mK - B C2S - C m5 - D m af + E  4 in which (mK) designates the KUHL module, (C2S) the module C2S, (mis) the silicic module, (mat) the aluminum-ferric module of the material to be ground and in which A, B, C, D and E are constants.  6. Method according to claim 5 for a clinker mill operating in open circuit, consisting of three compartments (9, 10, 11), characterized in that the following corrective coefficients are applied to the theoretical result (R)  - 0.1 for the first compartment (9),  - 0.2 for the second compartment (10),  - 0.15 for the third compartment (11).  7. Method according to claim 5 for a cement mill operating in a closed circuit, consists of three compartments (9, 10, 11), characterized in that the following corrective coefficients are applied to the theoretical resultant (R)  - 0.2 for the first compartment (9),  - 0.3 for the second compartment (10),  - 0.1 for the third compartment (11).  8. Method according to any one of the preceding claims, characterized in that during the grinding operation, is carried out in the different compartments (9, 10, 11) of the crusher (1), at regular intervals, samples of ground materials, and a control correction coefficient is defined which is applied to the theoretical result (R) from the comparison between the variations of the curve representative of the particle size of the material to be ground over the length of the mill ( Figure 3) and the curve representing the logarithm of the size of the grinding bodies over the length of the grinder (Figure 2).  9. Means for implementing the method according to any one of claims 1 to 8, characterized in that they comprise, for all of the compartments (9, 10, 11), means for calculating the theoretical result ( R), and for at least one of the compartments, means for calculating the corrected resultant (RC) and the overall useful surfaces of each size of grinding bodies1 from physical and / or chemical quantities characteristic of the material to be ground * and of data specific to the mill.