WO2007050078A1 - Procedes a haut rendement permettant de produire des microspheres a faible densite - Google Patents

Procedes a haut rendement permettant de produire des microspheres a faible densite Download PDF

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WO2007050078A1
WO2007050078A1 PCT/US2005/038980 US2005038980W WO2007050078A1 WO 2007050078 A1 WO2007050078 A1 WO 2007050078A1 US 2005038980 W US2005038980 W US 2005038980W WO 2007050078 A1 WO2007050078 A1 WO 2007050078A1
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primary component
microspheres
predetermined temperature
low
coal
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PCT/US2005/038980
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Steven A. Benson
Jason Laumb
Don Mccollor
Jim Tibbetts
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University Of North Dakota
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
    • B01J13/02—Making microcapsules or microballoons
    • B01J13/04—Making microcapsules or microballoons by physical processes, e.g. drying, spraying

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  • low-density microspheres are synthesized from precursor mixtures using a down-fired, entrained flow, high- temperature reactor, under partially oxidizing conditions and with a predetermined time- temperature profile so as to produce very high yields of low-density microspheres.
  • cenospheres Low-density microspheres, produced from and/or in the ash resulting from coal combustion (i.e., cenospheres), have unique properties that can be utilized in, among others, the building products industry to produce superior lightweight materials.
  • the properties of cenospheres are such that their applications in a multitude of industries are presently such that available sources are insufficient to meet demand, and harvested cenospheres regularly command very high prices.
  • the source of most cenospheres is pulverized coal combustion for electricity production, from which they are merely a byproduct.
  • the chemical and physical properties of cenospheres, the feed properties and reaction conditions that control their formation, and the cenosphere formation mechanisms themselves are presently unknown.
  • cenospheres based on feed (e.g., coal) composition and combustion conditions as well as determining other sources of cenosphere forming materials and the conditions that affect their formation.
  • feed e.g., coal
  • the fossil fuels may include coals of all rank, waste coal streams, petroleum coke, bitumen, and other carbon-rich fuels.
  • the synthetic mixtures may include precisely formulated mixtures of clays, carbons, and binding agents.
  • the process may comprise exposing the fossil fuel or synthetic mixture to a high temperature partially oxidizing environment for a controlled residence time.
  • Some embodiments comprise the synthesis of low-density materials with specific properties chemical and physical properties. Accordingly, certain embodiments of the invention relate to tailoring the properties of low-density microspheres manufactured from fossil fuels and synthetic mixtures to produce material with optimal properties for particular applications.
  • methods are described for producing hollow spheres with a diameter of up to 1000 ⁇ m from a primary glass-forming component comprising mineral matter derived from fossil fuels.
  • the primary component may comprise aluminosilicate materials derived from coal.
  • the methods preferably comprise one or more of the following steps: selection of coal or coal waste material and separation of aluminosilicate materials; separation of mineral matter from the coal source to concentrate aluminosilicate clays; addition of optional materials such as transition metals for color enhancement; grinding and sizing the feed material to provide a consistent particle size to the process; heating the clay and coal mixture in an entrained flow combustor at the proper time-temperature history to promote the formation of hollow particles; rapid quenching of the particles so as to trap the blowing agent in the sphere thereby creating a hollow particles.
  • the quenching is performed relatively rapidly and may be accomplished using gas, water, a combination thereof, or other materials and techniques as are known to those skilled in the art.
  • methods are provided for producing hollow spheres with a diameter of up to 1000 ⁇ m from synthetic glass-forming precursor mixtures.
  • the methods may comprise one or more of the following steps: selection of a glass-forming primary component, which may comprise an aluminosilicate; selection of a binding agent that wets the primary component at high temperature; selection of an optional blowing agent; selection of optional additive(s) to produce specific chemical and physical properties; grinding to provide an even distribution of binder and blowing agent throughout the particles; blending and/or slurrying the components in correct ratios; drying the formulation to produce a hardened material; grinding and sieving the dried formulation to produce precursor particles that may range from 25 to 250 ⁇ m in diameter; firing the particles at a temperature sufficiently high to melt the aluminosilicate material and to decompose or trigger the blowing agent; quenching the particles rapidly so as to trap the blowing agent in the spheres thereby creating a hollow particle or microsphere.
  • the primary component may comprise any aluminosilicate material, including without limitation one or more ashes, aluminosilicates, clays aluminosilicate clays, illite clays, or others), ceramics, glasses, silica gels, or any other type of aluminosilicate materials known in the art, and combinations of the above, providing that the conditions of the methods disclosed, which are described in more detail below, are met satisfactorily.
  • aluminosilicate material including without limitation one or more ashes, aluminosilicates, clays aluminosilicate clays, illite clays, or others), ceramics, glasses, silica gels, or any other type of aluminosilicate materials known in the art, and combinations of the above, providing that the conditions of the methods disclosed, which are described in more detail below, are met satisfactorily.
  • the binding agent typically wets, and reacts with, the primary component at high temperature.
  • the binder may comprise one or more alkali metal compounds or other materials known in the art subject only to the functions required for the binding agent as described in more detail below in accordance with the present disclosure.
  • the binding agent (or binder) may comprise sodium silicate.
  • it may be preferable to use no binding agent, in which case the primary component and binding agent are, in essence, the same material.
  • the optional blowing agent may comprise one or more materials that can volatilize or otherwise produce or release a blowing gas at conditions employed for the production of low- density microspheres in accordance with the present disclosure.
  • the blowing gas may assist in formation of cells or voids within a molten or semi-molten precursor.
  • the optional blowing agent may comprise carbon.
  • the optional blowing agent may be activated (by which it is meant that the blowing agent decomposes or reacts, releasing a blowing gas) at temperatures where the viscosity of the primary component is such that 2.8 ⁇ log ! o( ⁇ ) ⁇ 3.0, where ⁇ is expressed in poise.
  • methods for making low-density microspheres comprising heating a primary component at a operating temperature such that its calculated log 10 (viscosity, in poise) is between about 2.5 and about 3.0, in other embodiments between about 2.8 and 3.0 (inclusive), in conjunction with a binder having a calculated surface tension that is less than the calculated surface tension of the primary component, which is about 300 dyne/cm, at the operating temperature, and rapidly quenching the resulting low-density microspheres.
  • Some embodiments comprise preparing a particulate precursor as described above, comprising a primary component, a binding agent (binder), and an optional blowing agent; firing the precursor particles in a down-fired, entrained flow furnace, having one or more controlled temperature zones operating at predetermined peak temperatures, based on the precursor composition and desired microsphere properties; providing a precursor particle residence time at the operating temperature such that very high yields of low-density microspheres are produced; and rapidly quenching the produced microspheres to prevent their collapse.
  • methods are provided for producing hollow spheres with a diameter of up to 1000 ⁇ m from synthetic precursor particulate mixtures that may comprise silica or silica gel.
  • the methods may comprise selection of a fluxing agent, which may comprise an alkali oxide; selection of a binding agent, such as has been described above; selection of an optional blowing agent, such as has been described above; selection of optional additive(s) to produce specific chemical and physical properties; blending and/or slurrying the above components in correct ratios; drying the formulation to produce a hardened material; grinding and sizing the dried formulation to produce precursor particles preferably ranging from 25 to 250 ⁇ m in diameter; firing the particles in a down-flow, entrained-flow furnace, preferably at a temperature sufficiently high to melt the fluxed silica or silica gel material and decompose or trigger the blowing agent; quenching the particles rapidly so as to trap the blowing agent in the spheres thereby creating a hollow particle.
  • a fluxing agent which may comprise an alkali oxide
  • selection of a binding agent such as has been described above
  • selection of an optional blowing agent such as has been described above
  • the fluxing agent and the binding agent may comprise the same material.
  • the primary component, binding agent, and fluxing agent may have any chemical composition desired so long as certain performance criteria disclosed herein for the preparation of low-density microspheres are satisfied.
  • the synthetic precursor particulate mixture may comprise silica or silica gel, the fluxing agent/binding agent may comprise sodium silicate, and the optional blowing agent may comprise carbon.
  • the synthetic precursor particulate mixture may comprise silica or silica gel, the fluxing agent/binding agent may comprise sodium silicate, and the optional blowing agent may comprise sugar.
  • the synthetic precursor may be fired in an oxidizing environment at a predetermined temperature and with a fluxing agent concentration calculated such that the viscosity of the precursor at the firing temperature is less than about 1000 poise. In other embodiments the precursor may be fired under inert or even reducing conditions.
  • the surface tension of the binding agent in some embodiments may be less than the surface tension of the silica gel/flux mixture at the firing temperature and firing conditions. In an embodiment, the surface tension of the silica gel/flux mixture at the firing temperature may be about 303 dyne/cm.
  • the residence time of the precursor particles at the firing temperature may be from 0.5 to 2.0 seconds, and the microspheres produced therefrom may be quenched to below 900 0 C within about 200 msec, in other embodiments within about 120 msec, and in other embodiments within about 60 msec.
  • the binding agent and the fluxing agent may comprise the same compound or similar compounds.
  • the binding agent and the fluxing agent may comprise sodium silicate.
  • the invention provides that the precursor components may have any chemical composition whatsoever, so long as the appropriate physical/chemical criteria are met.
  • the physical and chemical property ranges for optimal low-density microsphere formation may be more important than the particular chemical composition of the components used to formulate the precursor mixtures, which may of course be varied as desired for particular applications, without departing from the scope of the invention.
  • the invention comprises apparatus capable of maintaining precursor particle residence times at temperatures where their viscosities may be 2.5 ⁇ logio ⁇ ⁇ 3.0 and in other embodiments 2.8 ⁇ logio ⁇ ⁇ 3.0, where ⁇ is in poise; and where the surface tension of tihe particles may be from about 285 to about 315 dyne/cm and in other embodiments from about 295 to about 305 dyne/cm and in still other embodiments less than about 300 dyne/cm.
  • the present invention thus provides several advantages over previously known techniques, including significantly higher yields of correspondingly lower priced, low-density microspheres with the desirable qualities previously obtainable only by harvesting cenospheres from the byproducts of coal combustion.
  • Fig. 1 is a block diagram illustrating a process for producing low-density microspheres from a fossil fuel such as coal.
  • Fig. 2 is a block diagram illustrating the process for producing low-density microspheres from synthetic materials.
  • Fig. 3 is a schematic diagram representing a down-fired tube furnace for production of low- density microspheres in accordance with the present disclosure.
  • Fig. 4 is a schematic diagram representing the flow scheme of a down-fired tube furnace used for production of low-density microspheres.
  • Fig. 5 is a cross-sectional diagram of a quench probe for use with a down-fired tube furnace for production of low-density microspheres.
  • Fig. 6 is a schematic diagram representing a large-scale down-fired furnace for production of low-density microspheres.
  • Fig. 7 is a scanning electron micrograph illustrating low-density microspheres.
  • Fig. 8 is a scanning electron micrograph illustrating low-density microspheres.
  • Fig. 9 is a scanning electron micrograph illustrating low-density microspheres.
  • Fig. 10 is a scanning electron micrograph illustrating low-density microspheres.
  • Fig. 11 is a scanning electron micrograph illustrating low-density microspheres.
  • U.S. Pat. No. 2,978,340 describes a method of forming glass microspheres from discrete, solid particles consisting essentially of an alkali metal silicate.
  • the microspheres are formed by heating the alkali metal silicate at a temperature in the range of 1000-2500 0 F in the presence of a gasifying agent, such as urea or Na 2 CO 3 .
  • a gasifying agent such as urea or Na 2 CO 3
  • These alkali silicate microspheres suffer from poor chemical durability due to a high percentage of alkali metal oxide.
  • Early methods for manufacturing hollow glass microspheres suffered from the use of expensive starting materials, resulting in microspheres that were necessarily expensive. Poor chemical durability also limited their utility.
  • Microspheres in various property ranges are also are generally available commercially from a variety of sources, for example 3M, Inc. (ScotchliteTM glass bubbles, ZeeospheresTM), Akzo Nobel (EXPANCEL® microspheres), and PQ Corp. (EXTENDOSPHERES®). Most commercially available supplies continue to suffer from the deficiencies of high cost and low strength. Thus most applications that justify commercial manufacture relate to glass microspheres and high-cost applications. Such microspheres are unsuitable for use as, for example, high-strength construction fillers.
  • the microspheres formed in flyash are usually between 20 and 300 ⁇ m in diameter ⁇ Mineral Impurities in Coal Combustion, Hemisphere Publishing Co., Washington (1985)), though particles as large as 500 ⁇ m have been reported by Sokol et al. ⁇ Fuel Processing Technology 67, 35-52 (2000)). It is generally recognized that some method of bubble formation is necessary to produce porous microspheres. Shibaoka and Paulson ⁇ Fuel 65 (1986)) have identified the mechanisms for the formation, and Benson ⁇ Laboratory Studies of Ash Deposit Formation During the Combustion of Western US Coals, Ph.D. dissertation, The Perm.
  • the chemical characteristics of the microsphere precursor materials may thus be postulated to have an influence on how the microspheres form, as well as their subsequent chemical and physical properties.
  • the composition of the precursor should be such that it provides a viscous liquid phase when exposed to high temperatures.
  • the viscosity of the material should be within an optimum range that will allow for the expansion of the sphere as a result of the carbon oxidation or mineral decomposition, hi addition, the chemical composition of the microsphere will influence the physical properties of the microspheres produced.
  • the physical properties include size, strength, shape, wall thickness, and color.
  • additives such as transition metals may produce sites on the cenospheres surface that have catalytic activity, and may thus provide reactive surfaces for better applicability in catalyst products.
  • the inorganic elements in coal occur as discrete minerals, organically associated cations, and cations dissolved in pore water.
  • the fraction of inorganic components that is organically associated varies with the coal rank.
  • Lower-ranked subbituminous and lignitic coals have high levels of oxygen. These groups act as bonding sites for cations such as sodium, magnesium, calcium, potassium, strontium, and barium (other minor and trace elements may also be associated in the coal in this form).
  • bituminous and anthracite the inorganic components consist mainly of minerals.
  • Mineral grains are usually the most abundant inorganic component in coal.
  • the major mineral groups found in coals, according to Raask include silicates, alumino silicates, carbonates, sulfides, sulfates, and phosphates, as well as some oxides.
  • the behavior of the mineral grains associated with coal during combustion can be predicted only from detailed information on the abundance, size, and association of the mineral grains in the coal.
  • the association of the mineral grain with the coal matrix must be determined and classified.
  • a mineral associated with the organic part of a coal particle is said to be “included”.
  • a mineral that is not associated with organic material is referred to as an "excluded” mineral.
  • the behavior of the organically associated elements that is, those elements that are atomically dispersed in the coal matrix, must also be measured as to their abundance in the coal. The organically associated elements will react and interact with the other ash-forming constituents during combustion. Methods to determine the inorganic composition of coal have evolved significantly over approximately the past 80 years.
  • SEM SEM and microprobe (energy dispersive x-ray analysis) analysis. Over the past 15 years, this technique has been used much more rigorously to determine the mineral component in coal.
  • CCSEM and automated image analysis (AIA) are the preferred techniques used to analyze polished cross sections of coal epoxy plugs.
  • the CCSEM technique is used to determine the size, shape, quantity, and quantitative composition of mineral grains in coals.
  • Quantification of the type and abundance of organically associated inorganic elements in lower-ranked subbituminous and lignitic coals is currently performed by chemical fractionation.
  • Chemical fractionation is used to quantitatively determine the modes of occurrence of the inorganic elements in coal, based on the extractability of the elements in solutions of water, 1 -molar ammonium acetate, and 1 -molar hydrochloric acid.
  • the filtered residues or solvent is analyzed after each leaching using x-ray fluorescence (XRF) to determine the percentage of each element remaining.
  • the non-extractable elements are associated in the coal as silicates, aluminosilicates, sulfides, and insoluble oxides.
  • the inorganic coal components undergo complex chemical and physical transformations during combustion to produce intermediate ash species.
  • the inorganic species comprise vapors, liquids, and solids. It is known in the art that the partitioning of the inorganic components during combustion to form ash intermediates depends upon the association and chemical-characteristics of the inorganic components, the physical characteristics of the coal particles, the physical characteristics of the coal minerals, and the reaction/combustion conditions. In order to predict the effects of inorganic constituents on combustion systems, much work has been undertaken in the prior art to elucidate the mechanisms by which the size and composition of intermediate ash species are formed.
  • inorganic constituents depends on the inorganic composition of the coal and combustion conditions.
  • the inorganic components can consist of organically associated cations, mineral grains that are included in coal particles, and excluded mineral grains.
  • mineral-mineral, mineral-coal, mineral-cation-coal, and mineral-mineral-cation-coal associations in coal are unique to each coal sample.
  • the physical transformations involved in fly ash formation include 1) coalescence of individual mineral grains within a char particle, 2) shedding of the ash particles from the surface of the chars, 3) incomplete coalescence due to disintegration of the char, 4) convective transport of ash from the char surface during devolatilization, 5) fragmentation of the inorganic mineral particles, 6) formation of cenospheres, and 7) vaporization and subsequent condensation of the inorganic components upon gas cooling. It is known in the art that because of these interactions, the resulting ash typically has a bimodal size distribution. The submicron component is largely a result of the condensation of flame-volatilized inorganic components.
  • the mass mean diameter of the larger particles is approximately 12 to 15 ⁇ m, depending upon the coal and combustion conditions.
  • Sarofim et al. refer to the larger-size particles as the residual ash because these ash particles resemble, to a limited degree, the original minerals in the coal ⁇ Combust. ScL Technol. 16 187-204 (1977)).
  • Processes such as ash mineral coalescence, partial coalescence, ash shedding, and char fragmentation during char combustion and mineral fragmentation all play an important role in the size and composition of the final fly ash.
  • Loebden and others J. Inst. Energy 119- 127 (1989)
  • Zygarlicke and others Prepr. Pap. — Am. Chem. Soc, Div. Fuel Chem.
  • Some coals such as lignites and subbituminous coals have exhibited a multi-modal size distribution with an intermediate size at 1-3 ⁇ m derived from the more refractory organically associated elements such as calcium.
  • Benson et al. examined in detail the effect of coal particle size and association of mineral grains (Ash Formation and Deposition Smoot, L.D. (ed.) Amsterdam: Elsevier, Ch. 4 299-373 (1993)). Also see Helble et al. ("Transformations of Inorganic Coal Constituents in Combustion Systems" US Dept. of Energy Pittsburgh Energy Technology Center, PSI-1024/TR-1141 (1991)). The transformations of excluded minerals are dependent upon the physical characteristics of the mineral.
  • Excluded minerals such as quartz (SiO 2 ) can be carried through the combustion system with its angular structure still intact. Excluded clay minerals can fragment during dehydration, melt, and form cenospheres.
  • the behavior of excluded pyrite depends upon its morphology. Some of the pyrite may be present as framboidal particles. Framboidal pyrite may fragment more easily than massive pyrite particles.
  • the decomposition of pyrite is very exothe ⁇ nic, and it transforms to pyrrhotite and oxidizes to FeO, Fe 3 O 4 , and Fe 2 O 3 during combustion.
  • the Urbain-derived models are based on the known behavior of network formers and modifiers, whereas the empirical models were formulated by fitting data for a few hundred measured viscosities.
  • the Senior 50/50 model performed well when the oxidation state and content of iron placed limitations on other models.
  • the Kalmanovitch and Sage and Mcllroy models appear most accurate for coals high in SiO 2 and lower in Fe.
  • Low-density microspheres are currently directly ⁇ i.e., intentionally) produced for applications such as relatively high-cost, but low-strength "microbubbles" for limited uses such as pharmaceutical delivery mechanisms and as experimental nuclear fusion fuel targets.
  • directly produced microspheres have relatively low strength and are relatively expensive, while naturally occurring byproduct cenospheres from coal combustion have high strength and are relatively expensive.
  • Directly produced microspheres are made from high cost materials using high cost equipment; indirectly produced microspheres must be harvested from immense piles of flyash in which they exist in but minuscule fraction.
  • low-density microspheres means roughly spherical particles, with diameter or longest dimension less than about 1000 ⁇ m, in other embodiments less than about 500 ⁇ m, generally at least partially hollow, with a bulk density generally less than about 2.2 g/cm 3 .
  • low-density microspheres There are many types of low-density microspheres.
  • the term “cenospheres” has historically been used to represent one type of material (hollow, glassy spheres) in fly ash that is thought to be produced (heretofore unintentionally) by partial or complete melting of coal mineral matter during the combustion process. Such microspheres comprise at most 1-2 weight percent of fly ash, and perhaps much less.
  • cenosphere and low-density microsphere may sometimes be used interchangeably, although "cenospheres” most correctly refers to low-density microspheres produced with flyash during pulverized coal combustion.
  • Some types of low-density microspheres produced by commercial concerns are also referred to as "microbubbles", or by other similar terms often intended to suggest some proprietary properties.
  • the primary component comprises a glass-forming material, or may preferably be selected based on its glass-forming characteristics.
  • silicates present in the fly ash of most Western low-rank coals are amorphous or glass-like.
  • a material characterized by one of skill in the art as a good glass-forming material is preferably one in which the rate of crystallization is slow with respect to the cooling rate. This fact has led many investigators to try to correlate the nature of the chemical bonds and the geometric shape of the crystals to the ease of glass formation.
  • Glass-forming oxygen polyhedra are triangles and tetrahedral, and cations forming such a coordination are considered in the art as network formers.
  • Alkali silicates form glasses easily, and the alkali atoms occupy random positions throughout the structure to provide charge neutrality.
  • the alkali and alkaline-earth elements added to a glass structure can be viewed as network modifiers which provide additional oxygen ions that modify the glass structure. This increases the oxygen-to-silicon ratio.
  • the addition of sufficient alkali and alkaline-earth oxides can cause a breakup of the network, which eventually leads to crystallization.
  • Glass-forming oxides sometimes referred to as network formers, have the ability to build and form three-dimensional, random networks.
  • Oxides that are good network formers include, but are not limited to, SiO 2 , B 2 O 3 , GeO 2 , P 2 O 5 , and AsO 4 . These network formers form highly covalent bonds with the oxygen atoms.
  • a network-modifying oxide is incapable of building a continuous network. The addition of such a modifying oxide to a network causes weakening of the network.
  • Good examples of network modifiers are oxides of sodium, magnesium, calcium, and potassium. Addition of a network modifier to a continuous network it breaks up the network by adding oxygen to produce non- bridging oxygens.
  • the addition OfNa 2 O to a silicate glass causes the formation of two non-bridging oxygens, one of which was contributed by Na 2 O, and the sodium ion balances the charge.
  • the addition of a network modifier to a silicate glass reduces the viscosity and increases the thermal expansion coefficient.
  • Some intermediate oxides are not capable of forming a glass, but can take part in the glass network.
  • a good example of an intermediate oxide is alumina.
  • the addition of a network modifier results in the formation of non-bridging oxygens and weakening the network.
  • Crystalline quartz and mullite along with a large amorphous glass phase are present in cenospheres and cenosphere-rich fly ashes.
  • the chemical composition of a fluid slag able to produce cenospheres also seems to be a composition that permits the crystallization of mullite and quartz from the amorphous phase.
  • the quartz and mullite may form small widely dispersed macrocrystalline patches on the cenosphere surface as a result of the devitrification of the cooling amorphous liquid phase or viscous liquid phase.
  • the types of crystals that form are dictated by the chemistry of the melt.
  • the formation of quartz and mullite for example, is characteristic of the cenospheres formed in pulverized coal combustion that are derived from illite minerals.
  • Cenospheres form commonly from both high- and low-rank coals and have been observed worldwide in thermal power systems. However, they seem to form within a relatively narrow chemical composition range, and a composition expected to have viscosities that are quite high.
  • the bulk fly ash has a similar chemical composition and viscosity to the cenospheres when cenosphere formation is significant. It is thus expected that the coal chemical composition will be similar to that of the cenospheres and fly ash for coals which produce significant numbers of cenospheres. It should thus, in theory at least, be possible to identify coals with the potential to produce cenospheres. Further, the narrow cenosphere composition range indicates that specific coal minerals are involved in cenosphere formation.
  • These minerals may be used in some embodiments of the present invention for economical production of low-density microspheres.
  • Carbon dioxide, nitrogen, and water have been identified as being encapsulated in cenospheres, and reactions producing these gases suggested as mechanisms for cenosphere formation.
  • cenosphere formation depends on the following criteria: the liquid material (e.g., molten ash or fiyash) may have a surface tension that is within a range sufficient to allow the formation of a molten particle and particle-to-particle wetting; a gas (blowing gas) may be present or generated inside a molten ash droplet in sufficient quantity to inflate the ash particle into a hollow cenosphere (the blowing gas may be provided by an optional blowing agent); the viscosity of the ash droplet may be low enough to permit the inflation to take place yet high enough so that the hollow droplet does not burst; the time- temperature history of the molten droplet may be such that the droplet is cooled before bursting and the cooling may be rapid enough that the hollow droplet does not collapse as the internal gas pressure decreases.
  • the operating conditions for production of low-density microspheres in accordance with some of the methods of the present
  • cenosphere formation An important clue to the mechanism of cenosphere formation is the presence of gases trapped inside cenospheres. These gases are presumably the blowing agent which inflates a molten ash particle to form a cenosphere. From the literature information on naturally occurring and synthetic cenospheres, CO 2 , CO, N 2 , H2O, and SO 2 are possible blowing agents. Volatilization of alkali inorganic species might also be considered a possible blowing agent. However, the range of cenosphere chemical compositions contains very little sodium, and the potassium appears to be incorporated in forms that are not volatile.
  • the presence of carbon dioxide may be the result of carbon oxidation, carbon gasification (along with CO), decomposition of carbonate minerals such as CaCO 3 , or diffusion of CO 2 into the molten slag.
  • Carbon monoxide can result from carbon oxidation or gasification as well as mechanisms described subsequently.
  • Water also can be the result of carbon gasification or oxidation, decomposition of hydrated and hydroxyl mineral species or outgassing of water trapped in pores of the coal.
  • Sulfur dioxide could result from the decomposition of sulfate minerals such as CaSO4 or from the oxidation of sulfides such as FeS 2 .
  • a potential complication in elucidating the source of the blowing agent is subsequent reactions of the encapsulated gas.
  • Water would be expected to react with alkali and alkaline oxides if present in the inner walls of the cenospheres to form the corresponding solid hydroxides such as CaO +H 2 O -> Ca(OH) 2 .
  • the presence of water could also be the result of infiltration through micro "pinholes" in the cenosphere walls, and not conclusively indicate water is the blowing agent.
  • Sulfur dioxide may also react readily with alkali and alkaline earth oxides on the inner cenosphere wall to produce solid sulfate species, removing SO 2 from the gas phase.
  • Carbon dioxide can also be produced as the result of carbonate mineral decomposition, such as for the case of calcium carbonate:
  • Water is known to be the blowing agent for the production of some synthetic cenospheres ("shirasuballoons”) from Shirasu volcanic glass.
  • the formation process involves milling the volcanic glass and treatment with hydrochloric acid to remove surface material, presumably to assist the adsorption of water.
  • Water is also used as the blowing agent in the production of some hollow ceramic oxide microspheres. Sulfur dioxide resulting from the oxidation of pyrite has been seen to produce hollow spherical particles similar to cenospheres, with the probable reaction being:
  • Sulfur trioxide resulting from the decomposition of sulfate species is also used extensively as the blowing agent in the production of synthetic glass microspheres.
  • Sodium sulfate is introduced into the molten high silica glass along with other additives to control viscosity. Control of the oxygen and SO 3 partial pressure over the melt permits the manufacture of synthetic hollow microspheres with a wide variety of densities.
  • Coal contains appreciable oxygen and hydrogen as well as carbon, as illustrated by the ultimate analysis of a typical Kentucky No. 9 coal, resulting in an empirical formula of C0.6H0.3O0.1N0.01S0.0 2 - Oxidation resulting from oxygen trapped as the slag becomes molten or oxygen diffusing into the slag would produce CO 2 and H 2 O along with small amounts of nitrogen and sulfur oxides. In an oxygen- deficient environment, gasification could also occur, producing CO and H 2 as well as CO 2 and H 2 O.
  • a typical product gas composition under strongly reducing conditions comprises approximately 60% CO, 30% H 2 , 8% CO 2 , and 2% H 2 O.
  • ⁇ P P - Pa - 2 ⁇ (l/r+ 1/rtf Eq. 8 where ⁇ is the surface tension of the slag r is the external sphere radius T 1 is the internal sphere radius
  • the initial slag volume and composition were provided from the ash particle-size composition distribution calculated by the ATRAN program.
  • the time-temperature history of the cenosphere formation is an input parameter dependent on the combustion/reaction system being modeled.
  • the ash compositions may be used to calculate viscosities as a function of temperature, preferably using the modified Urbain equation (Kalmanovitch et ah, Mineral Matter and Ash Deposition from Coal, Bryers, R. W., and Vorres, K.S., Eds., Engineering Foundation: New York, 89-101 (1990)), which is known in the art.
  • SiO 2 has a surface tension of about 303 dyne/cm, Al 2 O 3 about 313 dyne/cm, CaO about 310 dyne/cm, Fe 2 O 3 about 311 dyne/cm, MgO about 314 dyne/cm, K 2 O about 286 dyne/cm, and Na 2 O about 298 dyne/cm, as given in the Al-Otoom et al. (2000) publication cited above.
  • the surface tension has a weak dependence on temperature, so it can be approximated by a linear function of temperature using experimental measurements at a specific temperature as a reference point.
  • the surface tension is estimated to vary by about 4 dyne/cm for every 100°C change in temperature.
  • the excess pressure for the cenospheres is in the range of 0.09-0.58 atm (about 10 to about 60 kPa), with these values referring to room-temperature conditions.
  • a refined estimate of the final internal pressure may be obtained form actual cenosphere size and composition data.
  • Initial pressure and gas volume may then be estimated by back calculation. Alternatively, either the initial pressure and gas volume, or the rate of gas evolution, can be used as input variables, and a variety of gas evolution scenarios calculated.
  • Low-density microspheres may be produced from a wide range of materials.
  • the most common type of microspheres preferably comprises aluminosilicate glass materials.
  • the aluminosilicate glass materials may preferably be derived from mixed layered clays such as illite, montmorillonite, and kaolinite, although other sources as are known in the art may also be used successfully.
  • Silica gel may also preferably be used. These materials may rely on the presence of other elements such as sodium, potassium, calcium, magnesium, and iron as fluxing agents to reduce the viscosity of the materials and allow them to flow. These minerals are abundant in fossil fuels, and particularly in coal. In addition, various transition metals may be added to these minerals to change the chemical and physical properties of the low-density microspheres.
  • FIG. 1 shows mineral separation in block 10 that may be conducted with an air jig or similar device to separate the major minerals.
  • a density separation process for clay minerals may be incorporated into the air jig, as shown in Block 12.
  • the density separation process may be adjusted to provide a concentrated stream of clay-rich fraction.
  • Block 14 preferably involves the addition of transition metals to modify the chemical and physical properties of the clay materials, which are preferably added to the clay-rich fraction at Block 16.
  • Block 16 comprises size fractionating the combined material to provide feed streams of specific particle sizes to allow for the optimum formation of microspheres.
  • Block 18 describes the preparation of low-density microspheres by reacting the product of block 16 in, for example, a high temperature entrained flow reactor.
  • the high temperature entrained flow reactor may be adjusted to the composition of the precursors to provide the optimum temperature and time to produce the desired microspheres.
  • Block 20 describes represents separation of the low-density microspheres into preferred density (or other) fractions.
  • the materials for the formulation are first chosen as indicated at block 21, depending on the desired application for the low-density microspheres to be produced.
  • the formulation may comprise one or more aluminosilicate materials, one or more binding agents, and an optional blowing agent.
  • Other general formulations may of course be employed without departing from the scope of the invention.
  • the materials are then preferably mixed and ground to a specified size and slurried as indicated in Block 22.
  • Block 23 then preferably involves drying the slurry to removal all volatile matter that could rupture the microspheres during heating.
  • the dried material is then preferably ground and sieved to the appropriate size as shown in Block 24.
  • the sized particles are then fired as indicated in Block 25, in an entrained flow reactor that can be adjusted to control the particle residence time and temperature to produce low-density microspheres of desired properties. Rapid quenching of the microspheres is then preferably provided as shown in Block 26 to minimize the number of particles that burst.
  • the particle residence time and the temperature through the reactor and quench probe (up until the particles are quenched so as to cease reaction) is typically referred to as the "time- temperature history" or the "thermal history”.
  • the microspheres then may be separated according to size, density, color, and other properties, as indicated in Block 27.
  • Precursor Preparation With respect to selection and preparation of precursor materials, some embodiments for production of low-density microspheres comprise the following method.
  • binding agent and optional blowing agent, if used
  • the identification and selection of the binding agent is made preferably to ensure proper formation of the hollow microspheres.
  • the components are preferably selected with some care so as to prevent bursting of the forming microspheres and also to prevent the release of the blowing agent before the particles that will form the product microspheres are in the proper viscosity range for formation.
  • binding agents may include ashes, alkali metal compounds (such as sodium silicate), and others.
  • Illustrative blowing agents may include carbonaceous materials or any other materials capable of volatilization at appropriate conditions, as are known in the art.
  • Suitable primary components may include glass-forming materials, such as aluminosilicate materials, ashes, illite and other clays, glasses, silica gels, combinations of these materials, and others.
  • any optional additives to produce specific desired chemical and physical properties may then be made. This may be based on the need for the specific application, such as the addition of a transition metal colorant.
  • transition metals may by added as colorants to change the color of the glass microspheres.
  • addition of the metals at very low levels, preferably less than 1 wt-% of the product, will allow for modification of the microsphere color.
  • the addition of Cr, Mn, Cu, Fe, Co, Au, and combinations thereof may preferably be used to change the color of the microsphere. This addition may preferably enhance the use of the microspheres in specific applications.
  • colorants may be added as optional opalization agents.
  • iron or opalization agents such as SnO 2 may also be added to create colored microspheres and/or microspheres with desired light absorbing characteristics.
  • the material is preferably ground or otherwise comminuted to provide a uniform and even distribution of binder and blowing agent throughout the particles.
  • the aluminosilicate material may preferably be reduced to 5 ⁇ m to 8 ⁇ m diameter, and the blowing agent may preferably be reduced to less than 1 ⁇ m in diameter.
  • the above step may preferably be omitted.
  • the selection of the type of blowing agent preferably depends upon the temperature at which the viscosity of the primary component is such that 2.8 ⁇ logio( ⁇ ) ⁇ 3.0 ( ⁇ in poise).
  • the blowing agent may preferably be selected so as to devolatilize and release blowing gas when the primary component is within the above viscosity range, and one skilled in the art will recognize that many suitable blowing agents may be used without departing from the scope of the invention. If the binder is an insoluble solid it may preferably be reduced to less than 1 ⁇ m in diameter.
  • the components may preferably then be blended and/or slurried in the desired ratio for microsphere formation. Poorly formed spheres may result from too much or too little of either the binder or blowing agent.
  • the binding agent ranges from about 5 to about 25 wt-% (inclusive, dry basis), more preferably from about 5 to about 8 wt-% (inclusive, dry basis) of the total formulation.
  • the optional blowing agent(s) preferably range(s) from about 0.1 to about 1% (inclusive, dry basis) of the total formulation, if used.
  • the above formulation is then preferably dried to produce a hardened material.
  • the dried formulation may then preferably be ground or otherwise comminuted, and sieved or otherwise size- classified, to produce precursor particles preferably ranging in size from about 25 to about 215 ⁇ m in diameter.
  • the size of the precursor particles may preferably be varied to produce larger or smaller hollow microspheres. In some embodiments, narrower precursor particle size distributions may be preferred over broader size distributions.
  • some preferred embodiments of the present invention for production of low-density microspheres may comprise the following method.
  • the selection of coal or coal waste material is first made, followed by the separation of preferred aluminosilicate materials. Mineral matter is then separated from the coal, source to concentrate the preferred clays. If desired, optional materials such as transition metals may preferably then be added for the enhancement of color and and/or other microsphere properties.
  • the resulting material is then ground or comminuted and sized, preferably to provide a consistent and uniform particle- size feed material. This feed material is then preferably fired in a down-fired, entrained flow combustor, preferably having a predetermined time-temperature history to maximize the formation of low-density microspheres.
  • the low-density microspheres produced are then preferably rapidly quenched so as to trap the blowing agent in the solidifying microspheres, producing a dimensionally stable product. Quenching to 900 0 C or below is preferably accomplished within 200 msec, more preferably within 120 msec, and most preferably within 60 msec.
  • the time- temperature history of the combustor may be fixed or variable. Where multiple precursor materials are to be processed or where low-density microspheres with variable properties are desired, the time-temperature history may preferably be adjustable or controlled to achieve the desired product properties.
  • a down-fired, entrained flow reactor that is co-fired with natural gas may be used to produce the low-density microspheres.
  • the operating conditions including firing rate, maximum temperature, gas residence time, particle residence time, and gas cooling rates are all preferably carefully controlled based on the composition of the precursor materials.
  • the composition of the precursor material may preferably change depending upon the coal or waste coal source, or the aluminosilicate or other precursor material source.
  • the precursor particles are preferably fired at a temperature sufficiently high so as to melt the primary component material, which may preferably be an aluminosilicate material, a silica material (e.g., silica gel), or other primary component material, and decompose (trigger) the blowing agent.
  • the time-temperature history of the firing step is chosen to achieve the proper viscosity and surface tension conditions.
  • the range of temperature for typical aluminosilicates for example, is preferably from about HOO 0 C to about 1400 0 C, and varies depending upon the properties of the selected precursor materials.
  • the range of residence time is preferably from about 0.1 seconds to about 10 seconds, more preferably from about 0.2 seconds to about 2 seconds, and also may vary with the properties of the precursor materials.
  • a down-fired, atmospheric pressure drop-tube furnace suitable for the production low-density microspheres in accordance with the present disclosure.
  • the ADTF is a laboratory-scale, electrically heated, entrained-flow, tube furnace with the ability to treat precursors, combust coal, and produce ash and/or low-density microspheres under closely controlled conditions.
  • An advantageous characteristic of the ADTF is its ability to accurately simulate the thermal history of (ash) particles in larger scale processes.
  • a ' large variety of full-scale production reactor profiles can be quickly simulated to optimize full-scale conditions efficiently.
  • the ADTF is able to simulate full-scale furnaces to the extent that the time-temperature histories of the entrained particles can be accurately reproduced, and ADTF results are translatable to much larger down-fired, entrained flow furnace configurations that can achieve similar particle residence times and thermal histories, and should provide similar results.
  • the results obtained here from ADTF testing are, therefore, expected to be applicable to larger scale entrained-flow furnaces for production of low-density microspheres.
  • Entrained-flow furnaces for use with the methods of the present disclosure may be operated in a down-fired configuration in some embodiments.
  • the ADTF 100 is capable of maintaining gas temperatures up to 1600 0 C (2912°F) in each of four zones, comprising preheat section 110, top furnace section 120, middle furnace section 130, and bottom furnace section 140.
  • Precursor particles are injected to the alumina furnace tube 101 via water-cooled inlet 111 entrained in a primary air or gas stream, entering furnace tube 101 at injector outlet 102.
  • Secondary air or gas is provided to the annular space 121 and flows through flow straightener 115 to furnace tube 101.
  • Injector 105 which is water cooled, passes through preheat section 110, flow straightener
  • Preheat section 110 is heated by molybdenum disilicide heating elements 112 within alumina insulation 114 surrounding the injector 105.
  • Furnace sections 120, 130, and 140 are similarly configured, including Kanthal Super 33 elements 131 (typ) (with 90° bend) positioned around alumina furnace tube 101 and insulated with vacuum cast ceramic fiber 132 (typ) surrounded by containing steel shell 134 (typ).
  • Thermocouples 141 (typ) are provided as required to enable precise control of the temperature within the alumina furnace tube 101 in each of the sections (110, 120, 130, 140) of the furnace.
  • the furnace sections 110, 120, 130, and 140 are individually controlled via separate PLC controllers, as are well-known in the art, and corresponding thermocouples in each of the furnace sections.
  • Combustion/reaction parameters such as initial hot-zone temperature, excess air, residence time, and gas-cooling rate — can be closely controlled and monitored.
  • Treated materials, chars, ash, or microspheres can be collected after exposure to precisely-controlled temperatures for varying residence times to precisely control the time-temperature profile and therefore the thermal history of the particles.
  • Fig. 4 provides a schematic of the overall flow of the ADTF system, comprising the ADTF 100, quench probe 300, collection filter 210, and supplemental filter 220.
  • Vacuum pump 230 is used to preferably provide a slight vacuum on the quench probe 200.
  • Supplemental filter 220 protects vacuum pump 230 from possible contamination.
  • the outlet flow of vacuum pump 230 is measured by vacuum outlet flowmeter 240, which provides gas sample to CO analyzer 271, CO 2 analyzer 272, and O 2 analyzer 273, the flows to each of which are measured by CO flowmeter 261, CO 2 flowmeter 262, and O 2 flowmeter 263, respectively. Excess gas is vented to atmosphere.
  • Fig. 5 presents a detailed design sketch of quench probe 300, which comprises tube 325 surrounded by alumina insulating cylinder 320 and metal shield 330.
  • Quench port 310 provides for injection of cooling nitrogen into the hot exhaust from ADTF 100. Cooling nitrogen is fed to quench probe 300 via nitrogen inlet 350 into the water jacket 326 of tube 325. Cooling water enters cooling jacket 326 via water inlet 360 and exits via water outlet 365.
  • the residence time of particles within furnace tube 101 is controlled by the length to which quench probe 300 is inserted into furnace tube 101 from below.
  • low-density microspheres produced in furnace tube 101 are rapidly quenched by cool quench nitrogen via quench port 310 in quench probe 300, so as to trap the blowing agent in the microspheres, and solidified producing a dimensionally stable product.
  • Quenching to 900 0 C or below is preferably accomplished within 200 msec, more preferably within 120 msec, and most preferably within 60 msec.
  • quenching can be accomplished by means of nitrogen or other gas, water, a combination thereof, or other means known in the art without departing from the scope of the invention.
  • Collection filter 210 may comprise a filter as is known in the art for collecting ash in bulk or any size-segregating devices known in the art such as a University of Washington Mark 5 source test cascade impactor or a U.S. Environmental Protection Agency (EPA) Southern Research Institute five-stage cyclone.
  • EPA U.S. Environmental Protection Agency
  • Other collection devices as are well-known in the art may of course be used without departing from the scope of the invention.
  • Fig. 6 there is shown another embodiment of a down-fired entrained flow furnace in accordance with the present disclosure and suitable for the production of low-density microspheres.
  • the large-scale furnace 400 illustrated in Fig. 6 may be designed to down-fire about 2 kg/hr of solid feed via feed injector 410 to furnace tube 409 with a heat input of about 40,000 Btu/hr.
  • the solid feed material may be co-fired with natural gas, liquid, or solid fuels.
  • the furnace is preferably designed to maintain the flue gas (about 8 SCFM) generated by the combustion of the fuel at about 1500C for the first 4 m (12 ft) of the system, which is referred to as radiant zone 420.
  • the first 3 m (9 ft) section 430 of the heated radiant zone 420 has an inside diameter of about 15.2 cm (6 in) with the last heated zone 440 reducing down to 7.62 cm (3 in).
  • the radiant zone exit 450 is through a horizontal 3.8 cm (1.5 in) inside diameter ceramic tube.
  • a portion of any particulate material produced is removed prior to the convective section 460.
  • flue gas flows through an optional fouling test section 470, a cyclone 480 for final particulate removal with optional bypass line 490, exhausting through an air eductor and stack (not shown).
  • the large-scale furnace 400 is a sealed system maintained under a slight vacuum via the eductor.
  • the electrically heated furnace sections in radiant zone 420 have ceramic tubes (409 typ) exposed to molybdenum disilicide heating elements such as element 411 (typ) surrounded by high- temperature, fibrous insulating board 412.
  • Access to the inside of the large-scale furnace 400 is available at a number of locations such as port 414 (typ) in the radiant zone 420 for sampling and analyses. Ports such as 414 penetrate through a combination of cast, abrasion-resistant insulating refractory 413 and high-temperature fibrous insulating board 412.
  • a precursor formulation was prepared comprising approximately 75 wt-% silica gel and 25 wt-% sodium silicate with 0.1 wt-% sugar according to the following procedure.
  • Laboratory grade silica gel was ground in a small hammermill to a nominal 1-mm particle size.
  • 154 grams of sodium metasilicate (Na 2 SiOs ⁇ H 2 O) was dissolved in 200 ml distilled water. The solution was heated to approximately 38°C to facilitate dissolving the sodium silicate.
  • 0.269 grams of sugar (0.1% by weight of the anhydrous 25% sodium silicate + 75% silica gel) was added as a blowing agent. 200 grams of silica gel was slowly added to the sodium silicate solution with stirring.
  • the silica gel was observed to adsorb all of the solution turning to a viscous gel, which began to solidify.
  • the mixture was oven dried at 110 0 C for approximately 48 hours.
  • the gel was found to have solidified into large very hard lumps, with no evidence of the previous grinding discernable.
  • the mixture was broken into pieces able to be fed into a small hammer mill, where it was ground and the ground material sonic sieved to separate the desired particle size range. Oversize material was alternately reground and sieved.
  • the size range of the precursor particles as tested was approximately 150 -250 ⁇ m.
  • the resulting feed mixture was then fired in a down-fired, entrained flow, drop tube furnace (ADTF).
  • the ADTF feed rate was about 0.14 grams/min.
  • the ADTF gas flow was about 1 liters/min primary air with about 3 liters/minute nitrogen secondary gas.
  • the feed mixture was fired at multiple predetermined time-temperature histories as shown below in Table 1 and rapidly quenched to under 900 0 C within 200 msec.
  • Particle residence time was approximately proportional to drop height, with 46.5 cm corresponding to a residence time of about 0.7 seconds.
  • the calculated value of log ]0 ( ⁇ ) for the silica gel at 1300°-1325°C was approximately 3.0, the surface tension calculated for was about 303 dyne/cm, and the surface tension of the sodium silicate was marginally lower.
  • FIG. 7 is a scanning electron micrograph illustrating a cross sectional view of the low-density microspheres produced under the conditions of Example 1, which are representative of the microspheres produced with the formulation of Examples 1-6.
  • a precursor formulation was prepared as described in Examples 1-6.
  • the precursor was then fired as described above in the down-fired, entrained flow, drop tube furnace (ADTF), and rapidly quenched.
  • the peak temperature used was 1325°C, with a drop height of 62.5 cm, and a residence time of 0.94 sec, as shown in Table 2.
  • Sufficient precursor was fired to produce quantities of low-density microspheres sufficient for reliable measurement of the water-float yield of produced microspheres.
  • the bulk density of the low-density microspheres produced was 0.73 g/cm 3 .
  • the fraction of water-float material produced was 0.8533.
  • the water float yield of the microspheres produced was 85.33 wt-%.
  • Example 8 - Elite, No Binder, Large-Scale
  • a precursor formulation was prepared as described in Examples 1-6 except that illite was used with 0.2 wt-% coal, which was then slurried, dried, and pulverized to 106-180 ⁇ m. This material was then blended in a 90/10 (wt/wt) ratio with supplemental solid fuel. The supplemental solid fuel had a heating value of about 5500 Btu/lb. The resulting precursor-fuel mixture was then down-fired in the large-scale furnace at a feed rate of about 1.0 Ib/hr (approx.
  • the bulk density of the resulting low-density microspheres produced was about 1.71 g/cm 3 .
  • Scanning electron micrographs of the low-density microspheres produced are provided as Figs. 8- 11.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Dispersion Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Silicates, Zeolites, And Molecular Sieves (AREA)

Abstract

La présente invention se rapporte à un procédé permettant de synthétiser des microsphères à faible densité, qui consiste à traiter des précurseurs à des températures prédéterminées avec un historique temps-température contrôlé, de façon que l'on obtienne de très grands rendements de microsphères à faible densité. Les propriétés chimiques des composants des précurseurs permettent de calculer le comportement du précurseur, ce qui permet de sélectionner les conditions de fonctionnement et les composants de manière à optimiser le rendement et les propriétés du produit.
PCT/US2005/038980 2005-10-26 2005-10-26 Procedes a haut rendement permettant de produire des microspheres a faible densite WO2007050078A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101862266A (zh) * 2010-06-01 2010-10-20 中国人民解放军第三〇九医院 单分散性凝胶微球成型装置
JP2016006363A (ja) * 2014-06-20 2016-01-14 株式会社神戸製鋼所 ボイラの灰付着抑制方法、およびボイラの灰付着抑制装置

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US20040058576A1 (en) * 2002-08-15 2004-03-25 Lumberg Connect Gmbh & Co. Kg Card holder for smart-card reader
US20040079260A1 (en) * 2002-08-23 2004-04-29 Amlan Datta Synthetic microspheres and methods of making same

Patent Citations (2)

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Publication number Priority date Publication date Assignee Title
US20040058576A1 (en) * 2002-08-15 2004-03-25 Lumberg Connect Gmbh & Co. Kg Card holder for smart-card reader
US20040079260A1 (en) * 2002-08-23 2004-04-29 Amlan Datta Synthetic microspheres and methods of making same

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101862266A (zh) * 2010-06-01 2010-10-20 中国人民解放军第三〇九医院 单分散性凝胶微球成型装置
CN101862266B (zh) * 2010-06-01 2012-10-10 中国人民解放军第三〇九医院 单分散性凝胶微球成型装置
JP2016006363A (ja) * 2014-06-20 2016-01-14 株式会社神戸製鋼所 ボイラの灰付着抑制方法、およびボイラの灰付着抑制装置

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