Document NE492jn30Gk1kNn1xpVpynqkE

(5D11J) ESTABLISHED 1802 E. 1. d u Po n t d e Ne mo u r s & Co mp a n y INCORPORATED Wil min g t o n . De l a w a r e 19898 LEGAL DEPARTMENT CONFIRMATION COPY VTA ATRMATT. January 22, 1988 Uhthoff, Gomez Vega & Uhthoff Apartado Postal M-2059 06000 Mexico 1, D.F. , MEXICO Attention: Marisela Arhundia Acevedo Technical Department Gentlemen: Mexican Pat. Appln. No. 192468 Your Case 363-P Our Ref.: CH-1175 Coombe You are authorized to delete Claim 2 as well as Claims 3 to 6 as they are non-patentable under Mexican practice. Please amend Claim 1 to required form. The patent issued in the United States on March 5, 1985 as U.S. Patent No. 4,502,641. A copy is enclosed with this letter. Very truly yours, CHE:led Enclosure Craig M Evans N36764 DUPO50302035 United Stages Pntent [19] Coombe[45] Date of Patent: [I!] Patent Number: 4,502,641 Mar. 5, 1985 [54] FLUID ENERGY MILL WITH DIFFERENTIAL PRESSURE MEANS [75] Inventor: Anthony J. Coombe, McEwen, Tenn. [75] Assignee: E. L Du Pont de Nemours and Company, Wilmington, Del. [21] Appi, No.: 258,872 [22] Filed: Apr. 29, 1981 [51] Int. Cl.'............................................... B02C 19/12 [52] U.S. Cl................................... ..........241/5; 241/39 [58] Field of Search................... 241/33, 34, 5, 39, 30 [56] References Cited U.S. PATENT DOCUMENTS 2,032,827 3/1936 Andrews.............................. 83/46 2.783.947 3/1957 Hage .................................. 241/34 2.783.948 3/1957 Hage .................................. 241/34 3,380,665 4/1968 Jester et al................ .. 241/5 3,462,086 8/1969 Bertrand et al........ 241.'5 3,726,484 4/1973 Schurr ................................. 241/5 Primary Examiner--Mark Rosenbaum [57] ABSTRACT A fluid energy mill of the confined vortex type for comminuting pulverulent solids, said mill provided with means for measuring the differential pressure between the discharge and the feed of the mill through openings in the chamber peripheral wall and in the discharge means, each opening provided with means for purging into the mill to prevent pluggage thereof and a process for using the mill to grind solid TK>2 by maintaining a constant differential pressure between 100-600 inches of water. 5 Claims, 2 Drawing Figures N36764.01 DUP050302036 U.S. Patei^ Mar. 5,1985 4,502,641 $vs#!!j!2!Si?H 10 DUP050302037 4,502,641 12 Accordingly, it has now been found that in a fluid FLUID ENERGY MILL WITH DIFFERENTIAL energy mill of the confined vortex type for comminut PRESSURE MEANS ing pulverulent solids having in combination a disc shaped chamber defined by a pair of opposing circular DESCRIPTION 5 shaped axial walls and a peripheral wall, a multiplicity 1. Technical Field of inlets extending through the peripheral wall and The present invention relates to a fluid energy mill of aligned for directing gaseous fluid into the chamber the confined vortex type with a means for measuring the differential pressure across the mill and a process for tangentially to a circle whose radius is smaller than the radius, R| of the chamber, means for charging pulveru grinding particulate TiOr with the aforesaid energy mill 10 lent solids to the chamber at the peripheral wall and to achieve TiO: with improved gloss with efficient discharge means for withdrawing pulverulent solids utilization of energy. 2. Background Art and gaseous fluid along the axis of the chamber, the improvement wherein the fluid energy mill is provided Fluid energy mills of the confined vortex type are known and employed in industries such as pigment, cosmetic and plastic because of their efficiency and economy in comminuting particulate solids. U.S. Pat. No. 2,032,827 discloses designs of such mills in detail. Generally a fluid energy mill of a confined vortex type is disclosed in U.S. Pat. No. 3,462,086 as a variation of a basic disc-shaped chamber enclosed by two gener ally parallel circular plates defining axial walls with an annular rim defining a peripheral wall. The height of 15 20 with means for measuring the differential pressure be tween the discharge and feed of the mill through open ings in the chamber peripheral wall and in the discharge means, each opening provided with a means for purging into the mill to prevent pluggage. Furthermore, it was found that the grinding of TiO; pigment particles by feeding said particles into a fluid energy mill at a rate that will maintain a constant differ ential pressure within the fluid energy mill of from 100-600 inches of water resulted in advantages over prior known methods. the chamber axially being substantially less than the diameter. Around the circumference of the peripheral 25 In the case where superheated steam is the fluid en ergy that is fed to a fluid energy mill, the steam pressure wall are located a number of uniformly spaced jets for is converted to velocitv as the steam expands in the jets injecting a fluid, which furnishes the energy for commi and nozzles. The jets and nozzles are positioned around nution and one or more inlets for feeding the particulate the grinding chamber in such a way that the steam jets solids to be comminuted. The fluid and the particulate 30 force the steam and solid particulate to move in a vortex solids are injected tangentially to the circumference or a within the chamber. The speed at which the steam and circle that is smaller than the chamber circumference. A particulate solids travel around the chamber is the tan coaxial conduit in direct communication with the grind gential velocity. ing chamber is provided as a discharge means for the The tangential velocity decreases when the particu comminuted solids. In U.S. Pat. No. 3,726,484 paraxi- 35 late solids are introduced into the steam because the ally symmetrical discontinuities projecting from the solids are accelerated at the expense of the kinetic en axial walls of the chamber prevents the discharge of ergy of the steam. The greater the solids feed rate the oversized particles before they are reduced to the de greater the reduction in tangential velocity. Tangential sired size. velocity is further reduced by the additional friction in The flow of particulate solids to the mill has been 40 the case where the solids are more difficult to grind and controlled so as to permit efficient grinding of the are therefore retained in the grinding chamber longer. solids. Fluid energy mills combine grinding and classifi Tangential velocity is therefore a function of steam cation in a single chamber. As the fluid is fed tangen flow, pigment feed rate and pigment grindability. tially into the periphery of the chamber along with Grinding energy in the field of pigments has tradi solids to be comminuted, a vortex is created whereby 45 tionally been defined as the ratio of steam flow to solid the particles are swept along a spiral path to be eventu pigment feed rate (S/P) for fluid energy mills. From the ally discharged at the outlet. Generally the fluid feed preceding discussion it is evident that tangential veloc rate is maintained constant. Efficiency of grinding and ity is directly proportional to steam flow and inversely quality of the product where TiC>2 is being ground are proportional to the pigment feed rate, hence a direct affected by the ratio of the fluid feed rate to the particu 50 measure of grinding energy. Although tangential veloc late solids teed rate. ity cannot be measured directly, the differential pres Generally in the case of TiChthe flow of solids tends sure between the grinding chamber periphery and gas to be irregular when flow meters are used due to pig outlet can be measured and is, in fact, a function of ment buildup in the equipment for flow measurement as tangential velocity. Differential pressure therefore de well as buildup in the feed chute where measurements 55 fines the grinding energy. are taken. `Thus, solid feed rates can unknowingly be Control of differential pressure permits control of variable. This variability can result in inefficient energy grinding energy, which in turn controls product qual use and substandard product. The variability can have ity. In controlling differential pressure, pigment feed the same adverse effect on TiC)2 grinding even where rate is chosen as the manipulated variable. Pigment feed the flow meter is used to control the feed rate of Ti02 60 is chosen because of difficulties in measuring it directly, to the fluid energy mill. and because at constant steam rate where production is DISCLOSURE OF THE INVENTION maximized, the differentia! pressure becomes primarily a function of pigment feed. The speed of the pigment Now an apparatus has been discovered that avoids feeder is adjusted to maintain a constant AP. The con the adverse effects of the prior art and permits a more 65 trol action is inverse to the pigment feed since the differ efficient use of fluid energy for grinding and provides ential pressure is inversely proportional to the pigment an improved quality of product. The present apparatus feed rate. As differential pressure increases, additional is an improvement in the apparatus of the prior art. feed is provided by speeding up the feed of solids. The DUP050302038 ,4 502,641 34 increased feed rate decreases AP. Likewise, a drop in and fluid into the chamber vortex. The fluid is intro AP would require a decrease in the feed of solids in duced to the venturi by nozzle 10 and serves to entrain order to increase AP to the desired level. The feed rate and carry solids into the grinding chamber. The cylin can be manually changed or can be automatically ad drical discharge opening 6 carries fluid and ground justed. 5 solids out of the grinding chamber. Pressure tap line 12 As pointed out previously, differential pressure re senses the pressure in the discharge opening. Pressure sponds to changes in pigment grindability. If a pigment tap line 11 senses the pressure at the periphery of the becomes more difficult to grind, for whatever reason, grinding chamber. The AP is the differential pressure the differential pressure will be depressed and therefore across the mill. Purges with a non-condensable fluid are require a reduction in the feed of solids to the mill. This 10 applied to each pressure tap line to prevent pluggage occurrence of more difficult to grind solids heretofore thereof. The AP is maintained at the desired value by would pass unknown through the mill with the result adjusting the feed of solid material into the mill. that the particle size of the product would be too large The process of the present invention comprises feed and the gloss of the TiC>2 pigment would be too low. ing solid particulate T1O2 particles to the fluid energy Now for the first time the drop in AP can be used to 15 mil] described above. The fluid of the present process is avoid this decrease or loss in gloss. A drop in AP is a superheated steam. The flow of Ti02 solids to the mill warning that the pigment particles require more grind may be delivered by any of many known means, e.g., ing and therefore must be retained in the mill longer to belt feeder, screw feeder, pneumatic feeder, etc. The reach the required particle size. The ability to make means for solids delivery are not critical. The feed rate, corrections in feed rate based on AP therefore offers an 20 however, must be adjustable. The process of the present advantage over prior known operations in the achieve invention therefore comprises controlling the flow of ment of a uniform quality product. T1O2 solids and/or die flow of superheated steam to Additionally, control of solids feed rate with AP is provide a constant AP across the mill. However, it is more reliable than a manual control of solids that is preferred to control the flow of Ti02 solids and not the based on a direct measurement of the solids flow rate. 25 superheated steam flow so that production can be maxi Flow meters tend to be inaccurate. They are subject to mized. drift, plugging, fouling, etc. The pressure taps of this The AP across the mill must be held constant at a invention may also plug but the probability of pluggage pressure value of from 100-600 inches of water depend is less. This is due to the maintaining of a constant purge ing on the degree of comminuting of the T1O2 solids. flow through the tap lines. If, however, there is a plug- 30 The particular AP at which the process can be operated ging of the pressure tap lines, it will be apparent imme depends on the specific use for which the T1O2 is in diately. Corrective measures can be taken immediately tended, the gloss or particle size required and the geom to assure uniform quality of product. The grinding of etry and size ofthe mill. Accordingly, therefore, the AP the present process also permits a TiOj reduction in for some TiOz applications is 250-375 inches of water grinding energy of about 5-10% over that required 35 and 300-400 inches of water for others and 350-450 heretofore. inches of water for still others. The novel feature of the apparatus of the invention The apparatus of the present invention permits grind and the use of said apparatus to grind TiC>2 pigment is ing of particulate solids more efficiently. Apparatus of the concept of relating differential pressure to feed rate the prior art do not effectively provide as uniform a and the control of feed rate to provide constant AP 40 grind of solids and at as low steam to pigment ratios, across the mill. e.g,, a reduction of at least 5% in energy. DETAILED DESCRIPTION OF THE DRAWINGS The process of the present invention permits the grinding of T1O2 more efficiently and provides for the preparation of T1O2 having less of the larger more diffi The invention will be further described with refer- 45 cult to grind particles which results in improved gloss as ence to the drawings. well as more uniform gloss. The process also provides a FIG. 1 is a vertical cross section of the apparatus of more efficient use of energy, e.g., a reduction of at least the invention. 5% in energy as compared to conventional fluid energy FIG. 2 is a horizontal cross section of the apparatus of mills. FIG. 1 normal to the axis at the inlet jet level. 50 The description of the fluid energy mills described in Referring now to FIG. 1 and FIG. 2,1 is a source of U.S. Pat. Nos. 3,462,086 and 3,726,484 are hereby incor fluid, which in the case of superheated steam has tem porated herein by reference. perature and pressure controlling capabilities. The pre I claim: ferred fluid is superheated steam. A fluid header 2 encir 1. In a fluid energy mill of the confined vortex type cles the peripheral wall 4 of circular grinding chamber 55 for comminuting pulverulent solids having in combina 5. Nozzles 3, of which only three are shown, intercon tion a disc-shaped chamber defined by a pair of oppos nect the header and the grinding chamber. Each nozzle ing circular-shaped axial walls and a peripheral wall, a 3 enters the peripheral wall 4 of the chamber at an angle multiplicity of inlets extending through the peripheral such that the extension of the nozzle axis is tangent to a wall and aligned for directing gaseous fluid into the circle about the center of the chamber which has a 60 chamber tangentially to a circle whose radius is smaller radius smaller than the radius, R, of the chamber. A than the radius, R, of the chamber, means for charging multiplicity of these nozzles is advantageously used. pulverulent solids to the chamber at the peripheral wall The chamber 5 is shown to be relatively disc shaped, its and discharge means for withdrawing pulverulent actual dimensions being determined by the upper and solids and gaseous fluid along the axis of the chamber, lower circular plates 7 and 8 and peripheral wall 4. A 65 the improvement wherein the fluid energy mill is pro venturi feeding device 9 serves to introduce the solid vided with means for measuring the differential pres material to be ground to the chamber, it being aligned sure between the discharge and feed of the mill through somewhat tangentially to facilitate flow of the solids openings in the chamber peripheral wall and in the ( DUP050302039 56 discharge means each opening provided with a means 3. The method of claim 2 wherein the differential for purging into the mill to prevent pfuggage. pressure is 250-375. 2. A method of grinding TiCh pigment solids by feed 4. The method of claim 2 wherein the differential ing said solids into a fluid energy mill of a confined pressure is 300-400. vortex type at a rate that will maintain a constant differ 5 5. The method of claim 2 wherein the differential ential pressure across the fluid energy mill that is within pressure is 350-450. the range of 100-600 inches of water. 10 15 20 25 30 35 40 45 50 55 60 65 DUP050302040