US3020234A - Method and apparatus for producing a homogeneous thermal insulation mixture - Google Patents

Description

Feb. 6, 1962 w HAUMANN 3,020,234

METHOD AND APPARATUS FOR PRODUCING A HOMOGENEOUS THERMAL INSULATION MIXTURE Original Filed April 26, 1956 Annealing INVENTOR. WILFRIED HAUMANN A TTORNEY if T t :ij

3,Zb,234 Patented Feb. 6, i962 Maroon AND ArrAnArus FOR rnonuctuo Av noiuoosrtnous THERMAL msULATIoN Mrxruun Wiltried Haumann, Indianapolis, Ind, assignor to Union 5 This invention relates to an improved process of, and 1 apparatus-for rendering homogeneous, finely divided pulverized materials in large masses, in particular for the preparation of insulation mixtures.

Inthe production of an insulation mixture of ingredi- 1 outs having widely differing densities, a finely divided low heat conductive powder, such as silica, is thoroughly mixed with finely divided flakes of radiant heat barrier material, such as heat-reflective copper flakes. in mixing such pulverized materials for" forming a homogeneous mass, the usual practice is to stir the material by manual or mechanical means until the materials have thoroughly interspersed themselves to form a uniform composition. This procedure is costly and time consuming. In addition, because of the differences in densities between the components of the insulation mixture, there is a tendency for segregation to occur. As a conse'quenc, the insulation mass may not be in the desired homogeneous condition necessary to produce low heat conductive and low heat radiative" results. 3

According to the present invention, this difiiculty may be substantially overcome by preliminarily mixing the insulation ingredients consisting of low heat conductive powder and radiant heat. barrier particles in the desired proportions. The mixed insulation is then sifted to remove large'particle sizes; If tne reflectivity ofthe barrier particles is normally afiected by its outer oxide layer, as is the case with copper particles having oxide layers, the oxide layer may be reduced or removed by the'ac'tion of a chemically reducing medium such as hydrogen gas After this, the insulating mixture is put through a final mixing stage; which subjects the mixture to an intensecirculatory movement and turbulent action to produce intimate comminglingof the'insulating components, and uniform dispersion of the barrier particles, thereby en- 4 hancing' the heat insulating qualities.

It is, therefore, anim'portant object of the present invention' to provide animproved method and apparatus for expeditiously mixing several components into a homogeneous mass.

As shown in FIG. 1, an exemplary apparatus for carrying out the method of the invention may comprise generally cylindrical, elongated: mixing vat ill provided with one or more inlets 12 near the top thereof, through which raw materials composed of finely divided silica and copper particles may be tangentially introduced into the top of the vat in the desired proportions. These ingredients are pneumaticallymoved into vat it by means of air drawn through a pipe 14 attached to the top of the mixing vat 10, the pipe 14 having an exhausting or blower apparatus 16 inserted therein. The feed enters tangentially at 12, and the majority of the solid material falls down along the vat walls, due to combined centrifugal force and gravity. A vibrating screen filter 18 interposed between the top'of the vat it and the pipe 14 above the feed point of inlet pipe 12 retains and removes residual particles from the air.

Alternately, the ingredients may be roughly pro-mixed before entering vat It) by introducing measured proportions of the components into a separate blender (not shown). The exhauster i6 and screen 18 may then be associated with the blender, and the latter may be arranged to discharge its material by gravity through any suitable connection into vat it The raw material delivered into the vat it) falls by gravity tothc bottom of the vat consisting essentially of afrustowonically shaped hopper or base 2b provided'with' a lower outlet orifice 22. Connected to the outlet orifice 22 is a downwardly extending pipe 24 having a' control cockor star valve 26 for controlling the removal of in- 0 sulating material. Bridging of the vat contents is avoided Another important ob ect ofthe present 1nvent1on 18 to provide an'improved method and apparatusfo'r uniformly incorporating radiant heat'barrie'r particles" in a low heatconductive powderinsulation; 7 Other objects, features andadvantages" of the presentinvention will be apparent from the followin'gidetailed description of a preferred embodiment of the invention in which: 7 V FIG. 1 is adiagrammatic flow sheetj'of' a process" and apparatus embodying the principles of the invention" for" effecting homogeneous particle mixtures; and

FIG. 2- is an enlarged detail view, partly in section, of' the-mixer component employed in' the practiceofthe invention.

The invention will described in connection with the" production of an insulating mixture consisting of finely" 6 divided silica and copper'fl'akes'ofparticle -sizes less than 75 microns, but it is to be understood that the same prin ciples applyregardless of'the' natur'e of the particular iii-- gradients used, and are' thus applicable, for-instance, in the production of uniform mixtures having'two-or-nicre components of dififerent densities? by maintaining the entire vat in constant agitation as'by' means of a column agitator or vibrator ZS'secured thereto;

Insulating mixture from the vat it) passes onto an electrically driven vibratory feeder where it is advanced in an even stream along an'inclined'vibrating'pan so, which extends generally horizontally and slightly downwardly. The insulation mixture progresses to the discharge end' of thevibrating-pan 3b; where it is delivered into a hopper 32- ofa screen Sifter 31, which is fitted with affin'e mesh screen-fi l} preferably 200 mesh or less. The screen 34 is swept continuallyby an electrically driven spiral brush 33, andby this means particles tending to agglomer'ate or adheretogeth'er are're'duced to their basic particle sizes. Any foreign materials or oversized particlesof the ingredients are retained by-the screen, and are discharged; through waste chute 36. The line material passing" through the screen Tadtziils'intoa 'motor driven screw 'con v'eyor lit, which advancestheinsulating solids to thenext treatment station.

ln'thetre'atmentof insulation" mixturescontainingmetal powders; the insulation must be dried, and the metal should preferably be deo'xidized, particularly in the case of metals such as copper that are easily oxidiza-ble, and that should better: of oxide film-for satisfactory use. For combined dryingand deoxid'atio'n treatment, the copper silicainsulation mixture istransferred in o the bottom of a generally cylindricaL-hollow tubular fluidizat'ion'chamber 42 by means ofthe screw conveyor 48; Hot fluidizing' reducinggasconsisting preferably of 7% hydrogen and 93% nitrogen, andheated to approximately 450 C; is admitted into the bottom or the chamber '42 through an inlet conduit 45, lfrom'where itconveys the insulation mixture upwardly. The reducing gas may be discharged? from the top of'the fiuidization chamber through anoutlet 46. The resulting suspension of copper particles in Hot gas partially reduces the copper oxide, andincreases the reflective powers ol the copper'particles. 'ihe treatment also removes moisture from the powder; Comple- 0 tion of the powder drying andfreducing ofthepizrtiallyre duced'copperparticles is carried out-in heating coils'48 fitted-to the top of the" chamber 42, where the 'insulation mixture and carrier gas medium are electrically heated to between 280 C. and 360 C., and preferably about 350 C.

Reduced copper particles along with silica particles are removed from the heating coils 48 by a tubular conduit 50, and passed through a series of mixing mechanisms 52, which sequentially receive the gas-particle mixture for further and final mixing.

Each of the mixers 52 comprises a generally toroidal or donut-shaped hollow shell 53 having at one end an inlet opening 54 for the admission of fluidized mixture of spent reducing gas and entrained particles of silica and partially reduced copper, and at the other end an outlet opening 56 for the exiting gas-particle mixture, the outlet of one mixer being joined to the inlet of the next succeeding mixer by a suitable length of pipe 58. The material entering inlet 54 travels along oppositely directed arcuate paths 55a, 55b, which converge at the outlet 56. In the preferred practice of the invention each of the arcuate paths 55a, 55b should be generally of toroidal shape, extending over somewhat less than 180 so that the change of direction of the material entering or leaving the arcuate path is less than a 90 angle. The mixer 52 may be either elliptical or circular in cross section, the latter being preferred. Any number of mixers may be connected in series, four being illustrated in the drawing.

The mixer 52 automatically causes the fluidized mixture to be given a thorough and intimate mixing, and substantially eliminates the tendency for segregation with respect to like and unlike particles, and line and coarse sized particles.

In operation, the material entering the mixer 52 through inlet 54 is diverted into separate streams 55a and 55b, which together have an expanded cross section greater than the cross section of inlet 54, and are then converged at outlet 56 to their original cross section. Although the exact mathematical explanation of why intimate commingling is achieved in the mixer 52 is not entirely understood, the following theoretical explanation is believed to describe certain aspects of the mixing mechanism. The entering mixture is approximately homogeneously distributed across the cross section of the inlet tube 54-, and the individual particles pass through the mixer 52 in different paths, 55a and 55b, depending on their position relative to the center line of the inlet tube. In general, the particles near the center line of the tube are deflected to a greater extent by the inner and outer walls of the mixer, and experience more rotational flow characteristics than the particles entering the inlet tube 52 near the radial extremity of the tube, as shown in the drawing. The effect is that the radially outer particleswill pass through the mixer 52 faster than the central particles, the net result being a finite time delay or deceleration of one particle relative to another. For example, in operating with an average mixer throughput velocity of approximately 20 feet per second, or a mixer throughput time of 0.019 second, assuming an individual mixer length of 4.5 inches, some particles may pass through the mixer in one half the average throughput time or 0.0095 second. These fast moving particles will in turn mix with the particles entering the mixer 0.0095 second earlier with an 0.019 second throughput time. At the same time many of the particles will collide with each other, thereby influencing their throughput time. As a result, the particles of the material introduced into the mixer 52 are thoroughly and intimately commingled and segregation is substantially eliminated.

Optimum results may be obtained when the ratio of the inner minor axis A of the mixer to the diameter D of the inlet 54 is between 1.3 and 2.5, a ratio of 1.6 being preferred. In this respect the ratio of one-half the difference between the outer and inner minor axis to the inlet and outlet tube diameter should be in the range between 0.7 and 1.2, a ratio of 1.0 being preferred. Moreover, the ratio of the length of the mixer to the inlet diameter should not be less than 6.0. In addition, the solid constituent of the gas-particle mixture entering the mixer 52 should not constitute more than 10% of the mixer volume, and preferably between 5.5% and 6.7% of the mixer volume.

The intimately mixed powder from the mixer 52 is passed to a storage column 60, similar in construction to the mixing vat 10. Spent gas is drawn oil by a blower 62 through a vibrating screen filter 64 at the top of the storage column 60, and passed through an atmospheric cooling coil 66 to condense water formed by the reaction between the metal oxide and the hydrogen reducing gas. The water condensate is drained out through a separator 68 to prevent damage to the blower 62, and the thus dried gas exhausted through the blower 62 to the atmosphere. The top portion of the column 60 is provided with an insulating jacket 69 to prevent condensation of moisture formed in the deoxidation step and an entering of such moisture as normal moisture content of the air and ingredients.

To permit continuous operation and removal of the intimately mixed powder product from the system, a plate valve 70 connected to the storage column 60 is provided for withdrawal of powder from the bottom of the storage column 60 into a bagging device '72. A pulsating electromagnetic vibrator 74 is attached to the lower cone shaped hopper 76 to prevent clogging of the exits and bridging of powder either to or away from the cone wall.

In order to indicate still more fully the nature of the present invention, the following examples of typical procedures are set forth, it being understood that these examples are presented as illustrative only, and that they are not intended to limit the scope of the invention.

Equal quantities of silica particles and copper particles were pre-mixed, and the insulating mixture introduced into the vat 10. The insulating mixture was then screened through 80 mesh wire cloth screen, and passed into the chamber 42. The insulating mixture was then fluidized in a stream of annealing gas containing 93% nitrogen and 7% hydrogen, at a gas rate of to cu. ft./hr., the gas prior to admission in the chamber being at a pressure of approximately 22 p.s.i., and a temperature of 450 C. Only enough annealing gas was supplied at this gas rate to partially reduce the copper particles initially containing approximately 22% Cu O to about 5% Cu O. Thereafter, the gas-particle mixture was re-heated to 350 C. in the heating coils 48, and admitted into the mixers 52 at a velocity of approximately 20 ft./sec. After this, the commingled particles were separated from the spent carrying medium and tested. The thermal conductivity for this mixture at a density of 10.7 lbs./cu. ft. was 025x10" B.t.u./hr., sq. ft., F./ft. The same ingredients when well mixed in a conventional mechanical stirrer, had a thermal conductivity of 0.32 10- B.t.u./ hr, sq. ft., F./ft. Thus a 15.6% improvement in insulatron efliciency was achieved.

In a similar test the thermal conductivity of a partially reduced 200 mesh, 50% copper, 50% silica mixture havmg a density of 10.47 pounds per cubic foot was 0.l68 l0- B.t.u./hr., sq. ft., F./ft. A corresponding figure of 0.202 10- B.t.u./hr., sq. ft., F./ft. was obtained for the same partially reduced material when mixed by forceful screening. A comparison of the two on the latter basis indicates a 16.8% improvement in thermal conductivity by the method of the present invention.

From the above description, it will be seen that the method and apparatus of the present invention is effective in producing insulating mixtures having greatly improved insulating qualities. This is accomplished by mechanically pro-mixing the insulating ingredients, followed by fiuidization mixing, the fiuidization mixture being caused to travel along portions of a donut-shaped path.

It will be understood that modifications andvariations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

This application is a continuation of my copending application Serial No. 580,899 filed April 26, 1956, now abandoned.

What is claimed is: 1. In the production of a dry thermal insulation mixture of finely divided low heat conductive powder and I finely divided oxidizable radiant heat barrier material, a

high speed method of reducing the occurrence of segregation of said low heat conductive powder and radiant heat barrier material and improving the homogeneity thereof while preventing surface oxidation of said barrier material, said method comprising preliminarily mixing said low conductive powder and radiant heat barrier material in the desired proportions, sifting the mixture to deagglomerate any particles tending to adhere together, gas blowing the preliminary mix in a stream of hot reducing gas for a sustained traverse, and finally intimately mixing the hot gas blown particles by intense circulatory acceleration and turbulent action, and mechanically separating and removing the resulting mixture from the gas.

2. In the production of a dry thermal insulation mix ture of finely divided low heat conductive powder and finely divided oxidizable radiant heat barrier material, a high-speed method of reducing the occurrence of segregation of said low heat conductive powder and radiant heat barrier material and improving the homogeneity thereof while preventing surface oxidation of said barrier material, said method comprising preliminarily mixing said low conductive powder and radiant heat barrier material in the desired proportions, gas blowing the preliminary mix in a gas stream of nitrogen and hydrogen, finally mixing the gas-blown preliminary mix by passage thereof through alternately divergent and convergent reentrant paths, whereby said preliminary mix is subjected to an intense circulatory acceleration and turbulent action, and mechanically separating and removing the resulting mixture from said gas, thereby effecting an intimately commingled insulation mixture.

3. In the production of a dry thermal insulation mixture of finely divided low heat conductive powder and finely divided oxidizable radiant heat barrier material, the method of improving the homogeneity thereof while preventing surface oxidation of said barrier material, said method comprising preblending said low conductive powder and radiant heat barrier material, screening and entraining the mixture resulting from said preblending in a reducing gas, heating the entrained mixture, thereafter further mixing said entrained mixture in alternating divergent and convergent channels, and separating said entrained mixture from said reducing gas.

4. In the production of an insulation mixture of finely divided low heat conductive powder and finely divided radiant heat barrier material, a high-speed method of re ducing the occurrence of segregation of said low heat conductive powder and radiant heat barrier material and improving the homogeneity thereof, said method comprising preliminarily mixing said low conductive powder and radiant heat barrier material in the desired proportions, entraining the preliminary mix in a gas mixture of nitrogen and hydrogen, accelerating said mix-entrained gas in an intense circulatory movement and turbulent action along a toroidal path, and mechanically separating and removing the resulting insulation mixture from said gas.

5. Apparatus for the production of a homogeneous mixture of finely divided low heat conductive powder and radiant heat barrier material comprising a preliminary insulation mix supply container, a vibratory feeder for receiving insulation mix from said container and delivering said mix to a fiuidization chamber, sifter apparatus between said vibratory feeder and said fiuidization chamber to remove oversize particles, means for fiuidizing said mix in a reducing carrier gas, a series of toroidally shaped mixing chambers for turbulently moving said fluidized mix, and means for separating said carrier gas from the resulting mixture whereby an intimately commingled insulation mixture is effected.

6. In the production of a powder-like insulation mixture of finely divided low heat conductive powder and finely divided radiant heat barrier material having a density different from that of said powder, the method of improving the homogeneity thereof, said method comprising preliminarily mixing said low conductive powder and radiant heat barrier material in the desired proportions to form a loose mixture, gas-blowing said loose preliminary mix in a reducing carrier gas, accelerating said carrier gas and preliminary mix in an intense circulatory movement and turbulent action along a toroidal path and mechanically separating and removing the resulting loose, homogeneous mixture from said carrier gas.

References Cited in the file of this patent UNITED STATES PATENTS 441,163 Johns Nov. 25, 1890 1,977,300 Blunt Oct. 16, 1934 2,343,780 Lewis Mar. 7, 1944 2,399,984 Caldwell May 7, 1946 2,498,710 Roetheli Feb. 28, 1950 2,582,116 Goins Jan. 8, 1952 2,621,034 Stecker Dec. 9, 1952 2,833,838 Berg May 6, 1958 FOREIGN PATENTS 462,709 Germany July 17, 1928 72,473 Sweden Mar. 8, 1928

Claims (2)

1. 2. IN THE PRODUCTION OF A DRY THERMAL INSULATION MIXTURE OF FINELY DIVIDED LOW HEAT CONDUCTIVE POWDER AND FINELY DIVIDED OXIDIZABLE RADIANT HEAT BARRIER MATERIAL A HIGH-SPEED METHOD OF REDUCING THE OCCURRENCE OF SEGREGATION OF SAID LOW HEAT CONDUCTIVE POWDER AND RADIANT HEAT BARRIER MATERIAL AND IMPROVING THE HOMOGENEITY THEREOF WHILE PREVENTING SURFACE OXIDATION OF SAID BARRIER MATERIAL SAID METHOD COMPRISING PRELIMINARILY MIXING SAID LOW CONDUCTIVE POWDER AND RADIANT HEAT BARRIER MATERIAL IN THE DESIRED PROPORTIONS GAS BLOWIGN THE PRELIMINARY MIX IN A GAS STREAM OF NITROGEN AND HYDROGEN, FINALLY MIXING THE GAS-BLOWN PRELIMINARY MIX BY PASSAGE THEREOF THROUGH ALTERNATELY DIVERGENT AND CONVERGENT REENTRANT PATHS, WHEREBY SAID PRELIMANARY MIX IS SUBJECTED TO AN INTENSE CIRCULATORY ACCELERATION AND TUBULENT ACTION AND MECHANICALLY SEPARATING AND REMOVING THE RESULTING MIXTURE FROM SAID GAS THEREBY EFFECTING AN INTIMATELY COMMINGLED INSULATION MIXTURE.
2. 5. APPARATUS FOR THE PRODUCTION OF A HOMOGENOUS MIXTURE OF FINELY DIVIDED LOW HEAT CONDUCTIVE POWDER AND RADIANT HEAT BARRIER MATERIAL COMPRISING A PRELIMINARY INSULATION MIX SUPPLY CONTAINER A VIBRATORY FEEDER FOR

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