EP0094307A2 - Jet mills - Google Patents

Abstract

1. A jet crusher in which the granular and powdered material is continuously or discontinuously fed in an enclosure around which are disposed several nozzles (2, 3), arranged at differents levels and fed with a pressurized fluid insuring centripetal jets appreciably horizontal within the material in order to cause crushing areas by the impacts between the grains (attrition) and raise the most fine particles which are then permanently extracted by the top, whereas the bigger particles, because insufficiently crushed, laterally fall back into the material to be crushed, the big particles carry along with the fines being fed again in the crushing enclosure after sorting in the separator, characterized by the fact that the nozzles (2, 3) are fed with controlled pulses of gas by at least a distributor (34, 40) feeding alternately the different nozzles (2, 3).

Description

The present invention relates to improvements in jet mills in which the granular or pulverulent material is introduced continuously or not in an enclosure around which are arranged several nozzles supplied with pressurized fluid ensuring substantially horizontal centripetal jets within the material. to cause crushing zones by impacts between the grains (attrition) and cause the finest particles to rise, which are then continuously extracted from above, while the larger particles, because they are insufficiently crushed, fall laterally. in the material to be ground. The large particles entrained with the fines are reintroduced into the grinding chamber after classification in the separator.

Problem.

This involves grinding granular or powdery materials by subjecting the particles to impacts between the particles themselves (attrition). The speed of the particles is generated by a high pressure gas or vapor expelled through nozzles. -Gas or vapor can be inert towards the material to be ground.

State of the prior art and drawbacks.

The state of the art in the matter is clearly established by the American patent 1,948,609 of January 18, 1932.

In this patent, the material to be ground is introduced laterally into an enclosure around which are arranged nozzles which cause horizontal jets. which rise upward within matter. A version is provided where the nozzles are arranged annularly so as to concentrate their effect in the center of the enclosure.

The French patent ALPINE 2,104,091 reproduces the essentials of the American patent 1,948,609 cited previously.

In this grinder and in all grinders of this type, the gas or the vapor are injected continuously and the speed of the jet is generally supersonic. This continuous blowing has the disadvantage of creating zones of low material concentration since this material cannot be reintroduced with a suitable flow rate in the jet, in particular in the initial zone where the speed is the greatest. In addition, the particles are permanently animated with a movement with relatively high speeds and, consequently, the accelerations which they undergo are moderate when they fall in the zones of jets where there reign higher speeds.

In areas of low concentration, the frequency of shocks is relatively low, which decreases the intensity and efficiency of grinding on the one hand and energy efficiency on the other. The low acceleration decreases the relative shock velocities which also decreases the intensity and efficiency of the grinding.

• 1) par la mauvaise utilisation du jet, notamment dans sa zone initiale ;
• 2) par la vitesse élevée des mêmes particules qui ne sont pas accélérées.

The performance of the device is therefore weakened:

• 1) by the improper use of the jet, especially in its initial area;
• 2) by the high speed of the same particles which are not accelerated.

The present invention is intended to remedy these drawbacks.

Statement of the invention.

The crusher of the invention is mainly characterized by the fact that the nozzles are distributed at different levels and are supplied by pulses controlled by gas by at least one distributor supplying the different nozzles alternately.

In order to prevent the material from rising when the blowing stops upstream of the nozzle, which can lead to plugging and wear of the nozzle, provision is made for a continuous secondary blowing, at a reduced flow rate. This can be done by bypass.

In addition, the closure of the fluid flow to the nozzles can be obtained gradually.

For example, it is done by a rotary distributor with gradually reducing passage section. This is obtained by modulating the rotation of the distributor, or again by an appropriate passage section of the conduit in the rotary distributor. This section can be in a drop of water, for example, and reduce the flow rate at the end of closing.

According to a preferred embodiment, the nozzles are distributed in several series, each series being supplied by the same ramp external to the enclosure and each ramp receiving its separate, pulsed supply.

and alternated from the distributor. With this latter arrangement, it is possible to simultaneously supply either the nozzles of the same level or the nozzles of the same vertical,

either in an oblique (helical) distribution of part of the nozzles.

When the nozzles are supplied individually through the distributor, they can be supplied successively in a circular permutation. Said nozzles can also be arranged and supplied so as to act in a helical permutation.

The shape of the enclosure is varied. It can be cylindrical, prismatic, conical, pyramidal, barrel-shaped or any other form deemed appropriate. However, in some of these forms, and depending on the distribution of the nozzles, there may be areas where the material is insufficiently agitated. To remedy this, at least one secondary nozzle is supplied continuously.

As for the distributor supplying the different nozzles according to an established program but which can be varied, its operation is then controlled from a microprocessor device which thus manages the supply of the nozzles according to different criteria chosen by an operator .

Solution to the problem, advantages and industrial result.

Pulsed blowing allows materials to be reintroduced into the high speed areas of the jet while the blowing stops. Thus, upon resumption of blowing, the material is strongly accelerated; in this way, the blowing takes place every period in an area of high concentration of materials and its efficiency is improved.

The distribution of the nozzles and the pulses given to their supply are determined by the material, the initial fineness, the final fineness and the production to be carried out. In any case, it was found that production was improved with a reduction in consumption of energy.

The invention will be better understood with the aid of the following description which gives some nonlimiting examples of practical embodiment and which are illustrated by the accompanying drawings.

Brief description of the figures.

• La figure 1 est une vue schématique en perspective d'une première réalisation de l'enceinte avec des buses disposées suivant deux niveaux.
• La figure 2 est une vue schématique d'une autre enceinte avec les buses disposées suivant des génératrices verticales.
• La figure 3 est une vue d'une autre enceinte avec des buses disposées hélicoidalement.
• La figure 4 est une vue en perspective d'une enceinte avec des buses disposées suivant trois niveaux, chacun des niveaux étant alimenté par une rampe extérieure.
• La figure 5 est une coupe longitudinale axiale d'une réalisation de buses.
• La figure 6 est une vue schématique d'un by-pass d'une vanne d'alimentation pulsée d'une série de buses.
• La figure 7 est une vue schématique de l'ensemble d'une installation de broyage réalisée avec une enceinte de l'invention.
• La figure 8 est une coupe d'une valve à interruption de débit progressive.
• La figure 9 est une section droite du canal de distribution de la valve.

In these drawings,

• Figure 1 is a schematic perspective view of a first embodiment of the enclosure with nozzles arranged along two levels.
• Figure 2 is a schematic view of another enclosure with the nozzles arranged along vertical generators.
• Figure 3 is a view of another enclosure with nozzles arranged helically.
• Figure 4 is a perspective view of an enclosure with nozzles arranged along three levels, each of the levels being supplied by an external ramp.
• Figure 5 is an axial longitudinal section of an embodiment of nozzles.
• Figure 6 is a schematic view of a bypass of a pulsed supply valve of a series of nozzles.
• FIG. 7 is a schematic view of the assembly of a grinding installation produced with an enclosure of the invention.
• Figure 8 is a section through a valve with progressive flow interruption.
• Figure 9 is a cross section of the valve delivery channel.

Description of some embodiments.

The crusher of the invention is located in the center of an installation of which there is a General view in FIG. 7.

We recognize the grinding chamber (1), which here has the shape of a vertical cylinder but can have any other prismatic, conical, pyramidal or other shape which improves attrition and reduces the speed of the material at the walls . This grinding enclosure is surrounded by two ramps, one of the first level (4) and the other of the second level (5) which surround, like rings, the middle part of the enclosure (1). The ramps (4) and (5) feed nozzles, respectively (2) and (3). Each of the ramps (4) and (5) is fed in turn by the interme- _of iaire valves (6) and (7) that control supply all or nothing for each of the ramps (4) and (5 ) and therefore nozzles (2) and (3). The valves (6) and (7) are supplied, according to the arrows (20), (21) by pressurized gas or dry steam.

The ground material finely enough inside the grinding chamber (1) rises to the top and ends up in a separator (8) from which the finest particles are sent into a second separator (9) of finished products while the largest particles are returned to the screw conveyor (14) which supplies the grinding chamber (1) by the return pipe ( ¹ 1) and the lock (12). The gases having conveyed the products are sent from the separator (9) to the filter (10) which returns them to the atmosphere according to the arrow (22). The ground products are collected in (23) and (24).

The products to be ground are poured into the feed hopper (13) which is closed by a lock (25) and which opens into the screw conveyor (14) to feed the grinding chamber (1). The conveyor (14) has a sealing device (15) between the hopper (13) and the grinding chamber (1). The sealing device is advantageously constituted by an interruption of the screw inside the conveyor (14).

The product to be ground introduced into the grinding chamber (1) by the conveyor (14) falls on a porous bottom (17) under which there is an air chamber (18) to fluidize said product, in particular with a view to evacuating the unmilled material accumulated at the bottom of the enclosure (1) by the combination of the inclination of the bottom (17) with blowing air into said chamber (18). Uncrushed products are discharged through the lock (19). However, to avoid any accumulation of new products introduced by the conveyor (14), an auxiliary nozzle (16) is provided which blows gas continuously without releasing the outlet from the conveyor (14).

A line (26) is provided between the top of the enclosure (1) and the top of the hopper (13) to balance the pressures and facilitate feeding.

The essential characteristic of the device of the invention resides in the grinding chamber (1) where nozzles (2) and (3) are provided distributed at different levels and where the supply of said nozzles (2) and ( 3), by two separate ramps (4) and (5), is controlled by valves (6) and (7) whose operation depends on a distribution device which determines their alternating pulsating opening. Different variants in the food tation of the various nozzles and their distribution will be explained below.

FIG. 5 represents a longitudinal section of nozzles (2) which consist of a convergent of a divergent (28) connected by a neck (29) which is a narrow orifice. To prevent the neck (29) from becoming blocked by the materials inside the enclosure (1) when said nozzles (2) are not supplied normally, provision is made for a continuous supply at a reduced flow rate of the nozzles (2) using an appropriately sized bypass (30).

To obtain a gradual closure of the fluid flow to the nozzles (2), a rotary distributor (48) (FIG. 8) is used, the distributor channel (49) of which has a drop-shaped section as shown in FIG. 9.

Referring to Figure 1, there is shown a grinding enclosure (1) with nozzles (2) and (3) distributed over two different levels. The nozzles (3) of the upper level are supplied separately by conduits (31), (32), (33) themselves successively supplied by a solenoid valve (34) threaded from an electronic switch with adjustable frequency ( 35) to which it is connected by line (36).

Likewise, the nozzles (2) are supplied in successive pulses by the conduits (37), (38), (39) from a solenoid valve (40) whose operation is controlled by the electronic frequency switch adjustable (35) to which it is connected by the line (41). The compressed supply gas, generally air, arrives through the supply pipe (42), which can be isolated by the valve (43) and which supplies the two solenoid valves (34), (40). The electronic adjustable frequency switch (35) is advantageously accompanied by an adjustable calculator (35) is advantageously accompanied by a microprocessor computer which makes it possible to adjust the blowing time of each nozzle and the moment when this blowing will take place. All these times are adjustable so that we can manage at will the operation of each of the nozzles to create the maximum number of turbulence zones and move them at will in order to obtain the greatest possible efficiency in grinding.

In Figure 4, there is shown the same grinding chamber (1) with nozzles (3) supplied by a ramp (5) receiving compressed gas through the pipe (44). Also shown are nozzles (201) and (202) which are supplied either by ramps similar to the ramp (5), or individually as has been explained above and illustrated in FIG. 1.

The pipe (44) and each pipe leading to the nozzles (201) and (202) lead to solenoid valves (not shown) similar to the solenoid valves (34), (40) which are controlled by a switch similar to the switch (35). By acting on it, it is possible to cause successive, pulsating and intermittent grinding zones according to a desired cycle in different zones of the grinding chamber (1) in order to determine the maximum acceleration of the particles and their efficient grinding.

Referring to Figure 2, there is shown a grinding chamber (1) with its feed screw conveyor (14) and on the walls of which are distributed nozzles (203), (204), (205) and (206) according to verti wedges. The nozzles (203) can be supplied by the same ramp. It is the same for each of the nozzle groups (204), (205) and (206). Each of these ramps is then connected to a solenoid valve which distributes the air in the form of cyclic pulses according to the control of an electronic switch with adjustable frequency. In the same way as previously, each of the nozzles (203) to (206) can receive a supply by a separate pipe which also leads to a piloted solenoid valve in order to obtain the maximum of adjustment possibilities in the pulsations carried out.

Referring to Figure 3, there are shown nozzles (207) distributed helically at the periphery of the grinding chamber (1). The nozzles (207) can be supplied by one or more helical ramps which receive a supply of pulsed gas. Similarly as above, may also be provided a separate SUPPLY TERMINAL ^t ation of each of the nozzles (207) by means of a separate pipe which leads to a solenoid répartissan cyclic pulsations of gas following a program established by a adjustable frequency electronic switch.

All these variants make it possible to treat different powders with maximum efficiency. The distribution of the nozzles, their flow rate, the diameter of their venturi (29), the way in which they are supplied can thus vary at will to adapt to the materials, to the initial fineness thereof, to the final fineness that the 'we want to obtain and to the desired production.

Claims (10)

1. Improvements to jet mills in which the granular or pulverulent material is introduced continuously or discontinuously into an enclosure around which are disposed several nozzles (2), (3) supplied with pressurized fluid ensuring substantially horizontal centripetal jets at within the material to cause crushing zones by impacts between the grains (attrition) and cause the finest particles to rise, which are then permanently extracted from above, while the larger particles, because they are insufficiently crushed, laterally fall back into the material to be ground, the large particles entrained with the fines being reintroduced into the grinding chamber after classification in the separator, characterized by the fact that the nozzles (2), (3)
are distributed at different levels
and are supplied by pulses controlled by gas by at least one distributor (34), (40) supplying the different nozzles (2), (3) alternately. 2. Crusher, as defined in claim l, characterized in that the valve (6) supplying each nozzle is framed by a by-pass (30) of small section determining a continuous supply at reduced flow when said valve (6) is closed. 3. Crusher, as defined in claim 2, characterized in that the valve (6) is designed to obtain a gradual interruption of the flow of fluid by an appropriate passage section of the duct of the rotating distributor in the form of a drop of tapering water at the end of closing. 4. Crusher, as defined in claim l, characterized in that the nozzles (2), (3) are distributed in several series, each series being supplied by the same external ramp (4), (5) to the 'enclosure (1) and each ramp (4), (5) receiving its separate power supply, pulsed and alternated from the distributor (34), (40). 5. Grinder, as defined in any one of claims 1, 2, 3 or 4, characterized in that the nozzles of the same level (2), (3) are fed simultaneously. 6. Crusher, as defined in either of claims 1, 2, 3 or 4, characterized in that the nozzles (203), (204), (205), (206) of a even vertical are fed simultaneously. 7. Grinder, as defined in either of claims 1, 2, 3 or 4, characterized in that the nozzles (2), (3) are successively supplied in a circular permutation. 8. Crusher, as defined in either of claims 1, 2, 3 or 4, characterized in that the nozzles (207) are arranged and supplied so as to act according to a helical permutation. 9. Crusher, as defined in any one of the preceding claims, characterized in that at least one secondary nozzle (16) is supplied continuously. 10. Grinder, as defined in any one of the preceding claims, charac terized by the fact that the operation of the distributors (34), (40) is controlled from a device (35) with microprocessors which thus manages the supply of the nozzles (2), (3) according to different criteria chosen by an operator.

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