FI112782B - Process for industrial production of extremely fine powders - Google Patents

Description

112782

Process for the industrial production of very fine powders Förfarande för industriell Produktion av synnerligen fina Pulver

The present invention relates to a process according to the species definition 5 of independent claim 1, which is capable of producing economically, efficiently and dryly the fillers and finer coatings and pigments required by the process industry.

Currently, various types of 10 micronization methods based on the 1-phase principle are generally used to produce dry fillers and coatings for the process industry, as well as pigments. The equipment based on the 1-phase principle uses high-pressure, energetic working gas, compressed air, steam or some kind of shielding gas as the refining energy.

An integral pneumatic classifier, often equipped with a mechanical rotor, is often an integral part of a 1-phase micronizer. Phase 1-based processes generally work to

• ": the material to be raised is fed into the process in a step where only kinetic energy is accelerated by high pressure, e.g. 9 bar, or even 16 bar accelerated in separate gas nozzles, and consequently,. It is clear that the kinetic energy generated by the particles, despite the high pressure and energetic working gas, remains relatively low and the grinding efficiency poor. It is particularly difficult to produce products that require particulate matter of particular size using 1-phase technology. ; '£ 5 in the range of 0.2 to 5 microns or an average fineness of 0.2 to 5 microns, a precursor to industrial minerals.

:: ': 1 - phase grinding method is also rendered inoperative by the fact that as the particle size decreases, it becomes very difficult to classify the particles using a rotary pneumatic classifier because particles of less than 5 microns behave almost like gas due to their low mass.

2 112782 1-phase flow devices are also often constructed so that the grinding and grading take place in the same space and are also linked to each other through the amount of working gas. This is not a good thing because a small change in one of the two subprocesses may adversely affect the other subprocess. This type of constraint in current 1-phase principle devices severely limits the ability to produce industrial dry and medium fine end products of 0.2 to 5.0 microns economically and efficiently.

The object of the present invention is to eliminate the aforementioned disadvantages obtained by the method according to the characterizing part of independent claim 1.

Other features of the invention will be apparent from the dependent claims.

In the process of the present invention, the material to be ground is fed to the counter-jet mill by means of a double valve feeder. The intermediate valve in the double valve feeder uses a feed pressure higher than the actual milling pressure. Counter: · · The gas flow of the jet mill is interrupted or throttled for a short time when the · ·: lower valve of the dual valve feeder is opened. This operation ensures the efficient transfer of the low bulk material into the equalization tank of the counter-jet refiner, the remainder of which produces the desired gas / solids suspension from the material and energetic gas. The material is milled, depending on the material, by means of economically developed 1-8 bar working gas. The resulting energetic gas / solid suspension enables efficient utilization of the 2-phase current. ύ 5 background.

;: * The kinetic energy contained in the gaseous solids suspension can be effectively utilized and utilized in various refiner chamber units in a small volume, whereby the small particles are controlled by the high energy particles; · 3 0 ways. This is done by using different types of acceleration nozzles in the refiner chambers as needed. For example, conventional accelerating nozzles may be used in one unit and accelerating nozzles with degassing holes in the other. In this case, the units produce products with a different grain size distribution, which can be used to target 3,117,282 energy use for some grain sizes or to limit the production of some grain sizes.

In separate refiner units, the ground products may be kept separate or combined and stored in an intermediate container constructed in one or more refining circuits. The function of intermediate storage is to control the amount of internal circulation load of the refining circuit by mass monitoring. The production of ultra-fine particles of 0.2 to 5 microns, in this case autogenously, requires a high rotation load in the refining circuit, and it is reasonable to construct the volume required for the rotary load outside the actual refiner 10.

The bulk density of the material temporarily stored in the intermediate tank but in circulation is increased, which facilitates its efficient return to the back jet refiner.

15 From the intermediate tank or tanks, the material is also removed to the final product after the desired amount of circulation load on the refining circuit has been generated. Since all the material to be milled passes through the milling chambers of the counter-jet mill, the particles to be milled remain in the milling process min. 1 grinding cycle and max.

•, '·· for selected grinding cycles eg 7 cycles. The intermediate tank or tanks are dimensioned • '-20 so that the circulation load can be large even when needed and has a weighing system • ... · which is part of the process control. For example, the above container should contain the intermediate container. ·: In the case of a 7x feed size.

The amount of end product leaving is naturally the same as the amount of [55 new materials fed into the refiner. The use of an intermediate container enables the material to be recycled in a controlled manner and enables important, particularly hard-to-produce, 0.2 to 5.0 micron particles of solid minerals. produces more by using the number of grinding cycles required for grinding and, for example, various acceleration nozzles of geo: metric size.

'' ': 3 0 Depending on the material, the material returned from the intermediate tank to the counter-jet refiner is often very light in bulk. The bulk density may be up to 100 kg / m3. For this reason, it is advisable to seal the material in a separate press conveyor 4 112782 before feeding it into the counter jet mill. Increasing the bulk density significantly improves material handling.

If the final product has to be very fine and the bulk density of the material circulating in the closed circuit drops to a low level despite the screw sealing, two double valve feeders may be used with the counter-jet refiner. Thus, the consumption of gas for pressurization can be nearly halved by utilizing the gas to be removed for the initial pressure of the second feed tank.

10 The material taken from the intermediate tank to the final product may, if necessary, be treated with a separate mechanical grading device outside the refining circuit, the operation of which is not based on gas flows and the gas is not a controlling factor. With such a grading device, the largest particles of the final product can be controlled and returned to the counter-jet refiner with the raw material circulating through the intermediate container 15. The coarse-separated coarse product can be conveyed to the intermediate container by pneumatic transfer and the pressurized air released from the intermediate container of the double-valve feeder after initial pressurization can be utilized.

• 2 0 From a homogeneous raw material, which is preferably a material pre-ground in a mechanical refiner, an end product of unchanged quality can easily be produced. In this way, the milling according to the invention can be carried out in such a way that the proportion of the product having the required grain size of 0.2-5 μηι is increased. During recycling, coarser grain sizes also decrease. Because of this, 25 postclassifications are not always required. In order to ensure a consistent end product, a control unit can be connected to the equipment, programmed with the limit values for the most important micronization processes, such as; '- amount of raw material per unit time, - amount of finished product per unit time 30, - amount of working gas per unit time, and its pressure and temperature.

- amount of energy used to pressurize the working gas - amount of rotation load per time unit 5 112782

Because the critical parts of the refiner unit retain their shape for thousands of hours, a product of unchanged quality is produced at certain limits. If deviations from the limit values occur, the process is interrupted and the disturbance corrected. This simple system facilitates process utilization and quality control of the final product.

5

The invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1 shows an example of the apparatus used to carry out the method 10 of the invention, side view, and

Fig. 2 is a right side view of the apparatus of Fig. 1.

According to the invention, the material to be refined, optionally pre-ground in a mechanical refiner, is fed from the feed tank 1 into the double valve feeder hopper 15, from which it is periodically lowered to the double valve feeder container 3 after this upper valve 4 has opened. After receiving the batch of material, the upper valve 4 is closed and the intermediate tank pressurized to, for example, 5 bar, after which the lower valve 5 of the double valve feeder is opened and the pressurized material batch *: The lower valve 5 is then reclosed, after which the pressure in the intermediate container 3 is lowered to ambient pressure by introducing a pressurized gas "" "therein through a conduit 21. The upper valve 4 is then opened for a new batch of material from the hopper 2. I · '..' 2 with a pressurized working gas, for example 3.5 bar, to a gas-solid suspension, from a leveling vessel 6, the gas-solid suspension is accelerated, · by the working gas pressure, through In the counter-jet refiner 9, the milled gas-solid suspension is led through tubes 10 and 11 to a large intermediate storage 12 provided with a weighing system 13 for monitoring the amount of material collected therein. Namely, the solid 12 must collect a quantity of solids such that the system has sufficient circulation load to achieve the desired end product quality, which must be maintained throughout the milling process. The intermediate storage 12 is purged of air by means of blowers 14. Suitable filters 15 which prevent small particles of material from entering the open air. The solid collected in the intermediate storage 12 is somewhat compacted, which improves its handling when returned for refining with the new raw material 5. In order to achieve a very finely divided, low bulk product, the bulk density of the solid accumulated in the intermediate storage 12 can be further increased by means of a separate press screw conveyor 16. Circulation of the solids through the refining plant, together with the new feedstock from the feed tank 1, continues until the desired circulation load has been reached in the plant. After this, the process is continued so that as much new raw material is fed from the feed tank 1, which is ground together with the recycled solids from the intermediate storage 12, as the finished product 12 is discharged through the outlet pipe 17. This product can either be used as such, even in the case of lard, to a mechanical classifier 18 located outside the refining circuit where the largest particles 15 are separated from the final product. This separated coarse product is returned to the intermediate container 12 via tubes 19 for further refining. For the return of the coarse product, gas may be used from the intermediate valve tank 3 of the double valve feeder after initial pressurization: the gas to be released from the pressurized gas, which is passed along the pipe 20 to the collecting pocket of the classifier 18f.

According to a preferred embodiment, the apparatus has two parallel counter-jet refiners 9, 9a with its own feeders 2,2a; 3,3a; 4, 4a, 5; 5a, 6; 6a, 7,7a, which is advantageous, for example, when the bulk density of the material to be ground is low. In this case, it is desirable that one of the counter-jet refiners 9 is provided with conventional accelerator nozzles 8 and the other of the counter-jet refiner 9a is provided with accelerator nozzles with 25 gaseous discharge channels, wherein the refiner chamber itself is shaped differently. With this new type of refiner, it is possible to effectively control the refining conditions so that the final product in the desired grain size range is easily achieved.

Hereby, the double valve feeders of both refiner units can preferably be synchronized so that the rigid pressure remaining in the second double valve feeder container 3, after dispensing the material, can be utilized by the second double valve feeder container 3a after In this case, the gas consumption at the feed is almost halved. 1 ·

Claims (11)

A process for the industrial production of extremely fine powders, wherein the material to be ground is mixed with high pressure working gas into a gas-solid suspension which is passed through acceleration nozzles (8) to the chamber of a counter-jet chamber (9) for milling autogenous, pitch-drawn hence, the milled gas-solid suspension is passed to at least one intermediate container (12) belonging to the milling circulation, in which container gas is removed as the mixture is collected into the intermediate container (12), which is retumed to be ground together with new raw material until desired circulation load is present in the plant, after which the process continues so that finished product is removed therefrom as much as raw material is supplied to it. 2. A method according to claim 1, characterized in that the bulk density of the fastening substance collected in the intermediate container (12) is increased by means of a separate pressing screw conveyor (16) until it is returned to the counter-spraying chamber (9). 3. A method according to claim 1 or 2, characterized in that the material to be milled is measured to the counter thrust chamber (9) via a double valve feeder (3) and a leveling container (6), where feed pressure higher than 2 is used in the double valve feeder (3). the ordinary supply pressure and the flow of working gas in the counter thrust chamber (9) is stopped * ': or throttled during a torque when a sub-valve (5) is opened in the dual valve feeder. 4. A method according to claim 3, characterized in that the grinding is carried out at least in two counter thrust mills (9,9a), one having ordinary acceleration nozzles (8) and the other having acceleration channels provided with acceleration nozzles for efficient grinding of extremely fine material. 5. A method according to claim 4, characterized in that two parallel double valve feeders (3, 3a) are used for pressurizing and feeding the material to be milled, which is synchronized so that the pressure remaining in one of the double valve feeders (3.3a ) after delivery of a material kit can be used as starting pressure in the second double valve feeder: (3a, 3) after receiving a new material kit. 112782 Method according to any of the preceding claims, characterized in that the final product removed from the intermediate container (12) is guided to a separate mechanical grinding circuit (18) lying outside the grinding circulation, where the largest particles are separated from the final product and retumed into the intermediate container ( 12) for an additional grinding revolution. 5 7. A method according to any of the preceding claims, characterized in that, in order to ensure the uniformity of the quality of the final product, the device belongs to a control unit in which the unit has programmed the limit values for the most important parameters in the milling process, such as the amount of the raw material, the amount of the working gas, the pressure. and temperature, amount of energy used for pressurizing working gas and amount of circulating load. Process according to any of the preceding claims, characterized in that the grinding conditions are adjusted so that the final product contains the desired proportion of particles belonging to the powder class 0.2 - 5 µm. 9. A method according to claim 8, characterized in that the material to be milled is circulated in the process 2-10 times, preferably 4-7, in order to obtain the powder class for the final product which has been set up. 20 10. A method according to claim 6, characterized in that the coarse product which has been: separated by means of the sorter (18) is returned to the intermediate container (12) as a pneumatic conveyor by means of pressure gas which is discharged after the initial pressure setting from the intermediate container (3.3a) of the double valve feeder. : 25 Method according to any of the preceding claims, characterized in that,. as raw material is used material which has been ground by means of a mechanical grinder. • * I 30