ZA200603709B - A method for industrial producing of highly dispersed powders - Google Patents

Description

A METHOD FOR INDUSTRIAL PRODUCING OF HIGHLY DISPEERSED POWDERS

This invention relates to a mmethod according to the preamble of individual claim 1, by means of which it possible t-o produce for the processing industry necessary powders and coating agents and pigments- finer as before most economically, effectively and solid.

Currently, micronizing methods of different types based on the 1-pkase principle are in general use, by means of which methods solid powders and coating a_gents and pigments necessary for the processing industry are produced. In devices bas ed on the 1-phase principle as pulverizing energy high pressure energetic working g as, compressed air, steam or some shielding gas is used.

As essential part of the micronizing device based on the 1-phase tectanique there is often also a built-in pneumatic classifier often furnished with a mechanic=al rotor. Generally, processes working by 1-phase principle function so that the material to be pulverized is fed to the process in a stages, where in separate gas nozzles accelerateed kinetic energy is developed into corpuscles/particles to be pulverized, for instance by means of mere 9 bar or even 16 bar working gas, resulting in that they become pulveriz=ed to some extent.

Clearly the kinetic energy generated in the particles, regardless of high pressure and energetic working gas, remai ns quite small and the pulverizing effect poor. It is especially difficult to produce products by 1-phase technique, where especially corpuscles, the size of which is within the range 0,2 ~ 5 microns for instance of industrial minerals. Then the consumption/cost of energy increases quite strongly and the production capacity of the equipment drops.

The operation conditions of a functioning pulverizing method working by the 1-phase principle get worse, since while the size of the particles is g=etting smaller the classification of particles using a rotor-furnished pneumatic classifier becomes quite difficult, because as a mass thie particles under 5 microns behave almosst like gas.

Devices working by 1-phase flow are often so built that pulverizing and classification take place in the same place and are linked together also through the veolume of gas. This is not good, since a small change in either partial process may Imave a harmful effect on the other part of thes process. Restrictions of this type in present devices based on the 1- phase principle povwerfully restrict the possibilities to produce for the industry necessary solid end products and to their average fineness 02, - 5,0 microns economically and effectively.

The intention of this invention is elimination of the above present-ed disadvantages, which is accomplished by means the method according to the characte=rizing part of individual claim 1 of this inveration.

The other characteristics of this invention are disclosed in the depaendent claims,

According to the method of this invention the material to be pulverized is fed by a double-valve feeder to a counterjet pulverizer. In the intermedi ate tank of the double- valve feeder feed pxressure higher than the real pulverizing pressmure is used. The flow of working gas of the counterjet pulverizer is cut off or choked fom a short time, when the lower valve of the d ouble-valve feeder is opened. This measure erasures effective travel of material with low bulk density to the balancing tank of the coumnterjet pulverizer, in the end part of which the wanted gas-solids suspension is generaated from material and energetic working gas. Material pulverizing takes place, depen.ding on the matter, by means of economically developed working gas of 1-8 bar pressure. The generated gas- solids suspension makes it possible to utilize the 2-phase flow eff=ectively.

The kinetic energy contained in the gas-solids suspension can "be used and utilized in different pulverizing chamber units effectively in a small space, where also small particles are in the sphere of influence of high-energy particles in a controllable way. This takes place using in thes pulverizing chambers acceleration nozzles of different types as occasion demands. or instance, in one unit it is possible to use ceonventional acceleration nozzles in another winit acceleration nozzles furnished with gass outlet holes. Then the units produce as to Eheir granulate distribution different kinds of yoroducts, in other words thus it is possible to focus the use of energy on the production of =some particle sizes or to restrict the production of some particle sizes.

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Products pulverized in separate pulverizing units cara be kept separated or joined and stored in an Antermediate tank built in one or several pumlverizing spheres of influence. The function of imtermediate storing is to control by meanss of mass-monitoring the volume of circulation load. In this case, producing autogenously ultra fine 0,2-5 micron particles requires in thae pulverizing circle a great circulation load and it is wise to build the volume needed by th e circulation load outside the normal pulverizing equipment.

The bulk de=nsity of material momentary stored in the intermediate tank but being in circulation ri ses, which facilitates its effective backfeesd to the counterjet pulverizer.

From the intermediate tank or tanks removal of mate=rial is also started as end product after the warmted circulation load quantity is generated in the pulverizing circle. Since all material that- is to be pulverized moves through the- pulverizing chambers of the the counterjet pumlverizer the particles to be pulverized stay in the pulverizing process min. for 1 pulverizing circulation and max. for as long as chhosen circulations, for instance 7 circulations. The intermediate tank or tanks are so dimnensioned that the circulation load can be even quite big and have a weighing system, whi ch is part of the process control. In the above casse, for instance, the intermediate tank mus=st have room for material as much as 7x feed quantity.

Of course thee quantity of the removing end product is the same as the quantity of new material to bes fed into the pulverizer. The use of an inteermediate tank enables controllable circulation of the material and makes it also possible that important, especially of solid minerals with difficulty produced particles in the size of 0,2 —5,0 microns can be effectively produced in greater quantity using by pulverizing a necessary amount of pulverizing circulations and as to their geometry differeent acceleration nozzles.

Material to bwe returned from the intermediate tank to the counterjet pulverizer is often, depending ora the matter, very light as to its bulk density, which can be even under 100 kg/m?. Therefore it is worse to compress the material in a separate pressing screw conveyor before feeding into the counterjet pulveri=er. Increase of the bulk density improves the material handling significantly.

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If the end product must be highly dispersed and in spite of the scre=w compression the bulk density of material circulatimeg in closed circuit lessens it is possible to use in connection with the counterjet pulverizer two double-valve feed er. Then the gas consumption to be used can almost be halved in utilizing the removeable gas for initial pressurization of the tank of the other feeder.

The material to be taken as end product from the intermediate tank can, if necessary, be handled by a separate mechanical classifier outside the pulverizing cmrcle, the operating principle of which is not based on gas flows and the gas is not a factor controlling the operation. With such a classificatings device largest particles can be cortrollably separated from the end product and returned together with the circulating loacd to the counterjet pulverizer. Coarse product separzated by the classifier can be tramnsported into the intermediate tank as a pneumatic transfer, and as transport air pressu=xized air releasable can be used releasable after initia 1 pressurization. from the double-wsalve feeder of the intermediate tank.

Of uniform raw material, i.e. material advantageously prepulverizead in a mechanical pulverizer, an end product of unchamgeable quality can be easily produaced. In this manner it is possible to put pulverizing accerding to this invention into practice so that the share of product of necessary granular class 0,2 - S5®m increases. During Circulation also the coarser granular classes reduce. Thesrefore no reclassification is needed . In order to ensure uniform raw material a control uni® can be connected to the equipment, into which unit the limit values of most important factors connected to the micrommizing process are programmed, such as - quantity of raw material per time unit, - quantity of end product per time= unit, - quantity of working gas per time unit, and its pressure and temperature. - quantity of energy used for worl<ing gas pressurization - quantity of circulation load gas per time unit

Since the critical parts of the pulverizing unit retain their form for thousands of operation hours, by means of certain limit valtes a good quality product with unchangeable form can be produced. .If a deviation occwurs inthe limit values, the process is interrupted and

» the failure corrected. This simple system facilitates the use «of the process and the quality control of the end product. 5 Inthe following tlhe invention is disclosed with reference tow the enclosed drawings, where

Figure 1 shows ar example as a side view of an equipment used for utilization of the method according to the invention and

Figure 2 shows the equipment as per figure 1 from the righ t side.

Material to be pulverized or possibly pre-pulverized in a m echanical pulverizer according to the invention i s fed from feed tank 1 to feed hopper Z of double-valve feeder, from where it is let ste p-by-step to intermediate tank 3 of doubMe-valve feeder, when the tank upper valve 4 hass opened. After receiving the batch of masterial upper valve 4 is closed and the intermediate tank is pressurized, for instance to a pressure of 5 bar, whereafter lower valve 5 of dlouble-valve feeder is opened and the pressurized batch of material is by means of excess peressure forced to balancing tank 6, into w=hich feed of working gas from tube 7 is broken or choked for a while in order to facilitate the transfer of light material.

Then lower valve § is closed again, after which the pressumre of intermediate tank 3 is let to the level of environment pressure conveying the pressurized gas in it somewhere through tube 21. Then upper valve 4 is opened for a nevw batch of material from feed hopper 2. Material pulverized in balancing tank 6 is therm mixed with working gas, for instance pressurized in 3,5 bar pressure, into gas-solids suspension. From balancing tank 6 the gas-solids smuspension is accelerated by the effect of working gas pressure through acceleration nozzdes 8 of counterjet pulverizer 9 to the pulverizing chamber, where the material particles are autogenously pulverized on collidingg with high speed. Gas-solids suspension pulverized in countrjet pulverizer 9 is conveyeed through tubes1O and 11 to large-sized stock 12 furnished with weighing system 13 for control of the collected material quality. Namely, in intermediate depot such a quantity of solids must be collected that in the system there is a sufficient circulation load in order to achieve a wanted end produact, which sufficient circulation load muxst be maintained all the time during pulverizing process. Air is removed from intermediate tank 12 by means of suitable nozzles 714, which prevent the access of small rmaterial particles to open air.

Solids collected irto intermediate tank 12 tighten a little, which improves the handling of them, when returmed to for pulverizing together with new nriaterial. When aimed high dispersed product, the bulk density of which is low, the bulk density of material collected into intermediate tank 12 can still be raised by means of pressing screw conveyor 1.6.

Circmulation of solids through the pulverizing equipment together with new raw mater3al fed #rom feed tank 1 continues till in the equipmment the target load is reached. Then the proc=ess is continued so that from feed tank 1 ass much new raw material is fed, which is pulverized together with solids circulated frosm stock 12, as ready-made material is removed from intermediate tank 12 through exchaust tube 17. This product can be useed eithesr as such or in some cases conveyed ®o mechanical classifier 18 outside the pulverizing circle, where the greatest particles are separated from the end product. Thais separated coarse product is returned to intermeddiate tank 12 along tube 19 for additiormal pulveerizing. For return of the coarse product pressurized gas releasable from intermediate tank 3 of double-valve feeder can be used after Mnitial pressurizing which gas is conveyed along tube 20 to collection pocket of classifier 1B.

According to an advisable embodiment there are in the equipment side by side two coumterjet pulverizers 9,9a with own feed devices 2,2a; 3,3a; 4,4a; 5,5a; 6,6a; 7,7a, which is an advantage, for instance when the pulp derasity of material to be pulverized is lows.

Thera it is advisable that the one counterjet pullverizer 9 is furnished with convention al acceleration nozzles 8 and the other couraterjet pulverizer 9a is furnished with acceleration nozzles furnished with gas outlet channels, whereby also the pulverizirag chamber itself is shaped otherwise than pxesented in Finnish patent application 2002=0531.By means of this new type pulveri=zer the pulverizing conditions can mo- st effecztively be regulated so that the end prodwict of a wanted granule class is easilly achieved.

Them both the double-feed pulverizers can advaxtageously be synchronized so that when a material batch has been supplied the after-pmressure left in tank 3 of one double-feeed pulvesrizer can be made use of through tubes 21 and 21a as initial pressure of tank 3a ef the cwther double-feed pulverizer after receipt ofa new material batch when valve 23 Jn tube=20 is kept closed. Then the gas consumptiom in connection with feeding gets almo st halve=d.

Claims (11)

1. A method for industrial production of high dispersed powders, wh ere material to be pulverized is mixed with high pres sure working gas into a gas-solids suspension, which is through acceleration nozzles (8) conveyed to the pulverizing chammber of counterjet pulverizer (9) for autogenic pulverizing, characterized in that the puBverized gas-solids suspension is conveyed at least to one intermediate tank (12) in the “pulverizing circle, where the gas is removed from the blend and solids collected into inter—mediate tank (12), which are returned to be pulverized together with new raw material till there is in the equipment a wanted circulation lo ad, whereafter the process continuess so that as much material is removed from it as readfy product is added to it.

2. A method according to claim 1 characterized in that the pulp density of solids collected into intermediate tank (122) is raised by means of a pressing sc—rew conveyor (16) before returning the solids to counterjet pulverizer (9).

3. A method according to claim 1 or 2 characterized in that material ®o be pulverized is fed to counterjet pulverizer (9) tharough double-valve feeder (3) and balancing tank (6), whereby in double-valve feeder (3 ) a feed pressure higher than the regular feed pressure is used and the flow of counterjet pulverizer (9) working gas is broke=n or choked for a while, when the lower valve (5) of double-valve feeder is opened.

4. A method according to claim 3 characterized in that pulverizing is carried out at least in two counterjet pulverizers (9, 9a), whereby there is in one of thmem conventional acceleration nozzles (8) and in th e other acceleration nozzles furnisheed with gas outlet channels for effective pulverizing of high dispersed material.

5. A method according to claim 4 characterized in that for pressuriz=ing and feeding of material to be pulverized two dou ble-valve feeders (3, 3a) side by sicle are used, which are synchronized so that the after-pressure left after release of material in one of the double-valve feeders (3, 3a) can Me utilized as initial pressure of the other double-valve feeder (3, 3a) after receipt of new material.

6. A method ac=cording to any above claim characterized in that the end product removed from irmtermediate tank (12) is conveyed to- separate mechanical classifier (18) outside the pulve=rizing circulation circle , where the gareatest particles are separated from the end product and returned to intermediate tank (12) for an additional pulverizing circulation.

7. A method according to any above claim characte rized in that in order to ensure the uniformity of the end product quality there is in the equipment a control unit, into which the limit values of the most important parameters of the pulverizing process, as the quantity of raw material, volume, pressure and temperature, of working gas, quantity of energy used for— working gas pressurization and q wantity of the circulation load are programmed.

8 A method according to any above claim char=acterized in that the pulverizing conditions are reu glated so that there is in the end product a portion of particles aimed at in granular class @0,2 —5 pm.

9. A method according to claim 8 characterized in tlmat in the project the material to be pulverized is circmulated 2 ~ 10 times, advantageousl=y 4-7, in order to achieve the set granular class.

10. A method according to claim 6 characterized in that the coarse product separated by classifier (18) is returned to intermediate tank (122) as pneumatical transfer from intermediate tank €(3, 3a) of the double-valve feeder after initial pressurizing by means of release gas.

11. A method acco=rding to any above claim characteriz=ed in that material pre-pulverized by a mechanical pimlverizer is used as raw material.