US20070028509A1

US20070028509A1 - Coal particle compositions and associated methods

Info

Publication number: US20070028509A1
Application number: US11/496,263
Authority: US
Inventors: Robert Dobbs; Leonard Dolhert
Original assignee: Primet Precision Materials Inc
Current assignee: Primet Precision Materials Inc
Priority date: 2005-07-29
Filing date: 2006-07-31
Publication date: 2007-02-08
Also published as: WO2007016528A2; EP1934315A2; WO2007016528A3

Abstract

Coal particle compositions are provided. The coal particle compositions, in some cases, are characterized by having an extremely small average particle size (e.g., 1.0 micron or less) and a high average surface area (e.g., greater than 3 m²/g). The small particle size and high surface area can lead to significant property advantages including more efficient combustion, more effective fractional distillation, and enhanced pollution separation, amongst others. The coal particle compositions may be produced in a milling process that uses preferred grinding media (e.g., high density grinding media) to reduce feed coal particles to a desired final particle size. The coal particle compositions may be used in a variety of different applications including fuel and non-fuel uses.

Description

RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 60/704,040, filed Jul. 29, 2005, which is incorporated herein by reference.

FIELD OF INVENTION

The invention relates generally to coal and, more particularly, to coal particle compositions and methods associated with the same.

BACKGROUND OF INVENTION

Coal is a brown to black rock comprised primarily of carbon. Coal is formed by the accumulation and physical/chemical alteration of vegetation over long periods of time. Mining operations are used to unearth coal from the ground.
Coal may be used as a solid fuel to produce heat by combustion. The heat may be used to create steam which may power generators, for example, to produce electricity. Coal also has a number of non-fuel uses. For example, coal may be separated into smaller molecules in separation processes (e.g., fractional distillation) and then used to synthesize a variety of other types of chemicals and materials including polymeric materials, pharmaceuticals, specialty chemicals and oils, amongst others.
In certain processes, it may be desirable to process coal into particles. For example, fine coal particles may be mixed with a liquid to form a slurry for use as a fuel. Such slurries may be pumped through lines and pipes to facilitate transport and delivery of the fuel to desired locations.

SUMMARY OF INVENTION

Coal particle compositions and methods associated with the same are described.
In one aspect, a coal composition is provided. The composition comprises coal particles having an average particle size of less than 1.0 micron.
In another aspect, a coal composition is provided. The composition comprises coal particles having an average surface area of greater than 5 m²/g.
In another aspect, a method of producing a coal composition is provided. The method comprises milling coal feed particles to form a milled coal particle composition having an average particle size of less than 1.0 micron.
In another aspect, a method of producing a coal composition is provided. The method comprises milling coal feed particles to form a milled substantially non-porous coal particle composition having an average surface area of greater than 3 m²/g.
In another aspect, a method of producing a coal composition is provided. The method comprises milling coal feed particles using grinding media having a density of greater than 6 grams/cm³and an average size of less than 250 micron.
In another aspect, a method of producing a coal composition is provided. The method comprises milling a coal feed particle composition to form a milled coal particle composition from the coal feed particles; and, separating coal molecules from the milled coal particle composition at a temperature of less than 100° C. The separated coal molecules have a total weight of greater than 25% the weight of the coal feed particle composition.
Other aspects, embodiments and features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings. The accompanying figures are schematic and are not intended to be drawn to scale. For purposes of clarity, not every component is labeled in every figure. Nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. All patent applications and patents incorporated herein by reference are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a copy of an SEM micrograph of milled coal particles produced in Example 1.

DETAILED DESCRIPTION

The invention provides coal particle compositions. The coal particle compositions, in some cases, are characterized by having an extremely small average particle size (e.g., 1 micron or less) and a high average surface area (e.g., greater than 3 m²/g). The small particle size and high surface area can lead to significant property advantages including more efficient combustion, more effective separation processes, and enhanced impurity removal, amongst others. As described further below, the coal particle compositions may be produced in a milling process that uses preferred grinding media (e.g., high density grinding media) to reduce feed coal particles to a desired final particle size. The coal particle compositions may be used in a variety of different applications including fuel and non-fuel applications.
Coal particle compositions of the present invention may be produced at very small particle sizes. In some embodiments, the average particle size of the coal composition is less than 20 microns; in some embodiments, less than 10 microns; and, in some embodiments, less than 1.0 micron (e.g., between 10 nm and 1.0 micron). In certain embodiments, the average particle size may be even smaller. For example, the average particle size may be less than 600 nm, less than 250 nm, or less than 100 nm. In some cases, it is even possible to produce coal particle compositions having an average particle size of less than 50 nm, or less than 10 nm. Such particle sizes may be obtained, in part, by using grinding media having certain preferred characteristics, as described further below.
The preferred average particle size of the coal composition typically depends on the intended application. In certain applications, it may be desired for the average particle size to be extremely small (e.g., less than 100 nm); while, in other applications, it may be desired for the average particle size to be slightly larger (e.g., between 100 nm and 1 micron). In general, milling parameters may be controlled to provide a desired particle size, though in certain cases it may be preferable for the average particle size to be greater than 1 nm to facilitate milling. For example, the average particle size of the milled coal material may be controlled by a number of factors including grinding media characteristics (e.g., density, size, hardness, toughness), as well as milling conditions (e.g., energy, time).
It should be understood that the average particle size of a coal composition may be determined by measuring an average cross-sectional dimension (e.g., diameter for substantially spherical particles) of a representative number of coal particles. The particle size may be measured using a laser particle measurement instrument, a scanning electron microscope or other conventional techniques.
It should also be understood that coal compositions having average particle sizes outside the above-described ranges (e.g., greater than 20 micron) may be useful in certain embodiments of the invention.
The coal particle compositions of the present invention may also be relatively free of large particles. That is, the coal particle compositions may include only a small concentration of larger particles. For example, the D₉₀values for the compositions may be any of the above-described average particle sizes. Though, it should be understood that the invention is not limited to such compositions.
Coal particle compositions of the present invention may also have a very high average surface area. The high surface area is, in part, due to the very small particle sizes noted above. In certain embodiments, the coal particles may have surface pores (which may or may not extend through the particle) which can also contribute significantly to the surface area. Although, it should be understood that, in some cases, the coal particles are substantially non-porous being substantially free of such surface pores.
The average surface area of coal particle compositions may be greater than 1 m²/g; in other cases, greater than 5 m²/g; and, in other cases, greater than 50 m²/g. In some cases, the coal particles may have extremely high average surface areas of greater than 100 m²/g; or, even greater than 500 m²/g. It should be understood that these high average surface areas are even achievable in particles that are substantially non-porous. Such high surface areas may be obtained, in part, by using grinding media having certain preferred characteristics, as described further below.
Similar to particle size, the preferred average surface area of the coal composition typically depends on the intended application. In certain applications, it may be desired for the average surface area to be extremely large (e.g., greater than 50 m²/g); while, in other applications, it may be desired for the average surface area to be slightly smaller (e.g., between 50 m²/g and 1 m²/g). In general, milling parameters may be controlled to provide a desired surface area, though in certain cases it may be preferable for the average surface area to be less than 3,000 m²/g (e.g., for substantially non-porous particles). For example, the average surface area of the milled coal material may be controlled by a number of factors including grinding media characteristics (e.g., density, size, hardness, toughness), as well as milling conditions (e.g., energy, time).
The coal compositions of the invention are not limited to specific types of coal. That is, the invention encompasses all types of coal known in the art including sub-bituminous, bituminous, semi-bituminous, semi-anthracite and anthracite. “Coal compositions”, as used herein, may also refer to oil shale. “Coal compositions”, as used herein, are not meant to refer to compositions that have been precipitated from a solution comprising dissolved coal species. Although, it should be understood that “coal compositions” may include coal compositions that have been processed (e.g., during milling as described further below) to remove species from the coal composition.
One aspect of the invention is the discovery that coal particle compositions having the very small particle sizes (and high surface areas) described above can be produced in a milling process. The particle sizes (and surface areas) are achievable by using grinding media having particular characteristics. For example, in certain processes, it is preferred for the grinding media to have a very high density. It has been found that very high density grinding media can greatly enhance the efficiency of the milling process and can enable production of coal particle compositions having small particle sizes and high surface areas.
As described further below, the coal particles of the present invention can be produced in a milling process. Thus, these coal particle compositions may be described as having a characteristic “milled” morphology. Those of ordinary skill in the art can identify “milled particles,” which, for example, can include one or more of the following microscopic features: multiple sharp edges, faceted surfaces, and being free of smooth rounded “corners” such as those typically observed in chemically-precipitated particles.
It should be understood that the milled particles described herein may have one or more of the above-described microscopic features, while being substantially spherical, for example, when viewed at lower magnifications. In certain embodiments, it may be preferred for coal particles of the invention to be substantially spherical. In other cases, the milled particles may have platelet, oblate spheroid, and/or lens shapes. Other particle shapes are also possible.
It should be understood that not all embodiments of the invention are limited to milled particles or milling processes.
In some embodiments, it may be preferable for the particles to have a platelet shape. In these cases, the particles may have a relatively uniform thickness across the length of the particle. The particles may have a substantially planar first surface and a substantially planar second surface with the thickness extending therebetween. The particle thickness may be smaller than the particle width and particle length. In some embodiments, the length and width may be approximately equal; however, in other embodiments the length and width may be different. In cases where the length and width are different, the platelet particles may have a rectangular box shape. In certain cases, the particles may be characterized as having sharp edges. For example, the angle between a top surface (e.g., first planar surface) of the particle and a side surface of the particle may be between 75° and 105°; or between 85° and 95° degrees (e.g., about 90°). However, it should be understood that the particles may not have platelet shapes in all embodiments and that the invention is not limited in this regard. For example, the particles may have a substantially spherical or oblate spheroid shape, amongst others. It should be understood that within a milled coal particle composition, individual particles may be in the form of one or more of the above-described shapes.
As noted above, it may be preferred to use grinding media having specific characteristics. However, it should be understood that not every embodiment of the invention is limited in this regard.
In some embodiments, the grinding media is formed of a material having a density of greater than 6 grams/cm³; in some embodiments, greater than 8 grams/cm³; in some embodiments, the density is greater than 10 grams/cm³; or greater than 15 grams/cm³; or, even, greater than 18 grams/cm³. Though, in certain embodiments, the density of the grinding media may be less than 22 grams/cm², in part, due to difficulties in producing suitable grinding materials having greater densities. It should be understood that conventional techniques may be used to measure grinding media material density.
In certain embodiments, it also may be preferable for the grinding media to be formed of a material having a high fracture toughness. For example, in some cases, the grinding media is formed of a material having a fracture toughness of greater than 6 MPa/m^1/2; and in some cases, the fracture toughness is greater than 9 MPa/m^1/2. The fracture toughness may be greater than 12 MPa/m^1/2in certain embodiments. Conventional techniques may be used to measure fracture toughness. Suitable techniques may depend, in part, on the type of material being tested and are known to those of ordinary skill in the art. For example, an indentation fracture toughness test may be used. Also, a Palmqvist fracture toughness technique may be suitable, for example, when testing hard metals.
It should be understood that the fracture toughness values disclosed herein refer to fracture toughness values measured on bulk samples of the material. In some cases, for example, when the grinding media are in the form of very small particles (e.g., less than 150 micron), it may be difficult to measure fracture toughness and the actual fracture toughness may be different than that measured on the bulk samples.
In certain embodiments, it also may be preferable for the grinding media to be formed of a material having a high hardness. It has been found that media having a high hardness can lead to increased energy transfer per collision with product material which, in turn, can increase milling efficiency. In some embodiments, the grinding media is formed a material having a hardness of greater than 75 kgf/mm²; and, in some cases, the hardness is greater than 200 kgf/mm². The hardness may even be greater than 900 kgf/mm²in certain embodiments. Conventional techniques may be used to measure hardness. Suitable techniques depend, in part, on the type of material being tested and are known to those of ordinary skill in the art. For example, suitable techniques may include Rockwell hardness tests or Vickers hardness tests (following ASTM 1327). It should be understood that the hardness values disclosed herein refer to hardness values measured on bulk samples of the material. In some cases, for example, when the grinding media are in the form of very small particles (e.g., less than 150 micron), it may be difficult to measure hardness and the actual hardness may be greater than that measured on the bulk samples.
It should be understood that not all milling processes of the present invention use grinding media having each of the above-described characteristics.
Milling processes of the invention may use grinding media having a wide range of dimensions. In general, the average size of the grinding media is between about 0.5 micron and 10 cm. The preferred size of the grinding media used depends of a number of factors including the size of the coal feed particles, desired size of the milled coal particle composition, grinding media composition, and grinding media density, amongst others.
In certain embodiments, it may be advantageous to use grinding media that are very small. It may be preferred to use grinding media having an average size of less than about 250 microns; or, less than about 150 microns (e.g., between about 75 and 125 microns). In some cases, the grinding media may have an average size of less than about 100 microns; or even less than about 10 microns. Grinding media having a small size have been shown to be particularly effective in producing coal particle compositions having very small particle sizes (e.g., less than 1 micron). In some cases, the grinding media may have an average size of greater than 0.5 micron.
It should be understood that the average size of grinding media used in a process may be determined by measuring the average cross-sectional dimension (e.g., diameter for substantially spherical grinding media) of a representative number of grinding media particles. The grinding media size may be measured using conventional techniques such as suitable microscopy techniques or standard sieve size screening techniques.
The grinding media may also have a variety of shapes. In general, the grinding media may have any suitable shape known in the art. In some embodiments, it is preferred that the grinding media be substantially spherical (which may be used herein interchangeably with “spherical”). Substantially spherical grinding media have been found to be particularly effective in obtaining desired milling performance.
It should also be understood that any of the grinding media used in methods of the invention may have any of the characteristics (e.g., properties, size, shape, composition) described herein in combination with one another. For example, grinding media used in methods of the invention may have any of the above-noted densities and above-noted average sizes (e.g., grinding media may have a density of greater than about 6 grams/cm³and an average size of less than about 250 micron).
The above-described grinding media characteristics (e.g., density, hardness, toughness) are dictated, in part, by the composition of the grinding media. In certain embodiments, the grinding media may be formed of a metallic material including metal alloys or metal compounds. In one set of embodiments, it may be preferred that the grinding media are formed of ferro-tungsten material (i.e., Fe—W). In some cases, the compositions may comprise between 75 and 80 weight percent iron and between 20 and 25 weight percent tungsten. In some cases, ferro-tungsten grinding media may be carburized to improve wear resistance.
In other embodiments, the grinding media may be formed of a ceramic material such as a carbide material. In some embodiments, the grinding media to be formed of a single carbide material (e.g., iron carbide (Fe₃C), chromium carbide (Cr₇C₃), molybdenum carbide (MO₂C), tungsten carbide (WC, W₂C), niobium carbide (NbC), vanadium carbide (VC), and titanium carbide (TiC)). In some cases, it may be preferred for the grinding media to be formed of a multi-carbide material. A multi-carbide material comprises at least two carbide forming elements (e.g., metal elements) and carbon.
A multi-carbide material may comprise a multi-carbide compound (i.e., a carbide compound having a specific stoichiometry; or, a blend of single carbide compounds (e.g., blend of WC and TiC); or, both a multi-carbide compound and a blend of single carbide compounds. It should be understood that multi-carbide materials may also include other components such as nitrogen, carbide-forming elements that are in elemental form (e.g., that were not converted to a carbide during processing of the multi-carbide material), amongst others including those present as impurities. Typically, but not always, these other components are present in relatively minor amounts (e.g., less than 10 atomic percent).
Suitable carbide forming elements in multi-carbide grinding media of the invention include iron, chromium, hafnium, molybdenum, niobium, rhenium, tantalum, titanium, tungsten, vanadium, zirconium, though other elements may also be suitable. In some cases, the multi-carbide material comprises at least two of these elements. For example, in some embodiments, the multi-carbide material comprises tungsten, rhenium and carbon; in other cases, tungsten, hafnium and carbon; in other cases, molybdenum, titanium and carbon.
Suitable grinding media compositions have been described, for example, in U.S. Patent Publication No. 2006/0003013, which is incorporated herein by reference and is based on U.S. patent application Ser. No. 11/193,688, filed Jan. 5, 2006.
In some embodiments, it may be preferred for the multi-carbide material to comprise at least tungsten, titanium and carbon. In some of these cases, the multi-carbide material may consist essentially of tungsten, titanium and carbon, and is free of additional elements in amounts that materially affect properties. Though in other cases, the multi-carbide material may include additional metal carbide forming elements in amounts that materially affect properties. For example, in these embodiments, tungsten may be present in the multi-carbide material in amounts between 10 and 90 atomic %; and, in some embodiments, in amounts between 30 and 50 atomic %. The amount of titanium in the multi-carbide material may be between 1 and 97 atomic %; and, in some embodiments, between 2 and 50 atomic %. In these embodiments that utilize tungsten-titanium carbide multi-carbide material, the balance may be carbon. For example, carbon may be present in amounts between 10 and 40 atomic %. As noted above, it should also be understood that any other suitable carbide forming elements can also be present in the multi-carbide material in these embodiments in addition to tungsten, titanium and carbon. In some cases, one or more suitable carbide forming elements may substitute for titanium at certain sites in the multi-carbide crystal structure. Hafnium, niobium, tantalum and zirconium may be particularly preferred as elements that can substitute for titanium. Carbide forming elements that substitute for titanium may be present, for example, in amounts of up to 30 atomic % (based on the multi-carbide material). In some cases, suitable multi-carbide elements may substitute for tungsten at certain sites in the multi-carbide crystal structure. Chromium, molybdenum, vanadium, tantalum, and niobium may be particularly preferred as elements that can substitute for tungsten. Carbide forming elements that substitute for tungsten may be present, for example, in amounts of up to 30 atomic % (based on the multi-carbide material).
It should also be understood that the substituting carbide forming elements noted above may completely substitute for titanium and/or tungsten to form a multi-carbide material free of tungsten and/or titanium.
It should be understood that grinding media compositions that are not disclosed herein but have certain above-noted characteristics (e.g., high density) may be used in embodiments of the invention. Also, it should be understood that milling processes of the present invention are not limited to the grinding media compositions and/or characteristics described herein. Other suitable grinding media may also be used.
In general, any suitable process for forming grinding media compositions may be used. In some cases, the processes involve heating the components of the composition to temperatures higher than the respective melting temperatures of the components followed by a cooling step to form the grinding media. A variety of different heating techniques may be used including a thermal plasma torch, melt atomization, and arc melting, amongst others. For example, one suitable process involves admixing fine particles of the elements intended to comprise the grinding media in appropriate ratios. The stability of the mixture may be enhanced by introduction of an inert binding agent (e.g., which burns off and does not form a component of the grinding material). The mixture may be subdivided into a plurality of aggregates (e.g., each having a mass approximately equal to that of the desired media particle to be formed). The aggregates may be heated to fuse (e.g., to 90% of theoretical density) and, eventually, melt individual aggregates to form droplets that are cooled to form the grinding media.
In some embodiments, the grinding media may be formed of two different materials. For example, the grinding media may be formed of a blend of two different ceramic materials (e.g., a blend of high density ceramic particles in a ceramic matrix); or a blend of a ceramic material and a metal (e.g., a blend of high density ceramic materials in a metal matrix).
In some embodiments in which the grinding media comprises more than one material component, the grinding media may comprise coated particles. The particles may have a core material and a coating formed on the core material. The coating typically completely covers the core material, but not in all cases. The composition of the core and coating materials may be selected to provide the grinding media with desired properties such as a high density. For example, the core material may be formed of a high density material (e.g., greater than 8 grams/cm³). The core, for example, may be formed of a metal such as steel or depleted uranium; or a ceramic such as a metal carbide.
As noted above, coal particle compositions may be produced in a milling process that use grinding media as described herein. The processes may utilize a wide range of conventional mills having a variety of different designs and capacities. Suitable types of mills include, but are not limited to, ball mills, rod mills, attritor mills, stirred media mills, pebble mills and vibratory mills, among others.
In some cases, conventional milling conditions (e.g., energy, time) may be used to process the coal particle compositions using the grinding media described herein. In other cases, the grinding media described herein may enable use of milling conditions that are significantly less burdensome (e.g., less energy, less time) than those of typical conventional milling processes, while achieving a superior milling performance (e.g., very small average particle sizes).
One aspect of the invention is that the small coal particle compositions of the invention may be produced using very low specific energy input (i.e., energy consumed in milling process per weight of feed material).
Milling processes of the invention can involve the introduction of a slurry of feed coal material (e.g., feed particles) and a milling fluid (e.g., water or others described further below) into a processing space in a mill in which the grinding media are confined. The viscosity of the slurry may be controlled, for example, by adding additives to the slurry such as dispersants. The mill is rotated at a desired speed and coal material particles mix with the grinding media. Collisions between the coal particles and the grinding media can reduce the size of the coal particles. In certain processes, it is believed that the mechanism for particle size reduction is dominated by wearing of coal particle surfaces; while, in other processes, it is believed the mechanism for particle size reduction is dominated by coal particle fracture. The particular mechanism may affect the final characteristics (e.g., morphology of the milled coal particle composition). The coal particles are typically exposed to the grinding media for a certain mill time after which the milled coal material is separated from the grinding media using conventional techniques, such as washing and filtering, screening or gravitation separation.
It should be understood that, in certain methods, the goal of the milling process may be to accelerate a reaction involving coal particles rather than to reduce particle size. In these methods, coal particle size also may be reduced, though the particle size reduction may be negligible in some cases. In methods that accelerate reactions with coal particles, reactivity may be enhanced by wearing particle surfaces and, thus, exposing reactive species. In some cases, layer(s) on the coal particles that may otherwise impede reactions may be removed in the milling process.
In some processes, the coal slurry is introduced through a mill inlet and, after milling, recovered from a mill outlet. The process may be repeated and, a number of mills may be used sequentially with the outlet of one mill being fluidly connected to the inlet of the subsequent mill.
In certain processes, it is possible to reduce the size of coal particles and solid impurity particles (e.g., pyrite) at different rates. For example, coal particles may be reduced at a much higher rate than solid impurity particles (e.g., pyrite) and, in certain processes, the impurity particles may be only be negligibly reduced. In this manner, the milled coal composition may include small coal particles and larger impurity particles. This enables efficient removal of the coal particles from the impurities by conventional physical separation techniques such as screening or density floatation methods.
This selective particle size reduction may be accomplished by controlling milling parameters such as the rotational speed (rpm) of the mill which is a measure of milling intensity. For example, the rotational speed (or milling intensity) can be selected so as to efficiently reduce the size of the coal particles, while not efficiently reducing the size of the impurity particles. Though suitable rotational speeds (or milling intensities) may depend on the specific process (e.g., specific type of coal being processed), those of ordinary skill in the art can readily determine suitable values by varying the rotational speed and observing the effect on the wear rate of the coal and impurity particles.
The small coal particle sizes and high surface areas also enable efficient removal of chemical impurities including organic impurities (e.g., organic sulfur) and/or low vapor pressure impurities. For example, the small particle size and high surface area enhances access to such chemical impurities by suitable chemicals which can react with the impurities to form reactants that are subsequently removed from particle surfaces. Also, the small particle size and high surface area promotes removal of low vapor pressure impurities from the particles (e.g., by desorption) which may be at particle surfaces or can readily diffuse to surfaces. The chemical impurities may be removed during, or after, the milling process.
Accordingly, processes of the invention enable production of coal particle compositions having low levels of both physical and chemical impurities. For example, processes of the invention may reduce impurities such that the compositions include less than 0.1% by weight of such impurities. Although, it should be understood, that not all compositions of the invention have such low impurity levels.
In certain processes, the milling fluid may be selected to provide additional functions. For example, the milling fluid may be capable of reacting with the small coal particles during the milling process, itself (i.e., a reactive milling process). This can eliminate additional processing steps and can limit handling of fine coal particles which may be advantageous in certain cases.
The milling fluid may be a suitable solvent that is capable of extracting desired chemical species from the coal. For example, the milling fluid (e.g., light cycle oil (LCO)) may be capable of extracting a refined chemical oil (RCO) from the coal. The resulting product obtainable from the milling process can include small coal particles, as well as a mixture of RCO and the milling fluid (e.g., LCO). Such a product can be used to produce jet fuel (e.g., JP-900)
In certain embodiments, a gas may be dissolved in the milling fluid. The gas may be capable of reacting with the coal particles.
In another process, the milling fluid may be a hydrocarbon fuel, such as petroleum. The mixture of the small coal particle composition and the fuel can be processed to form a high quality coke.
Some processes involve milling the coal particles in an environment that provides hydrogen capable of reacting with the coal particles. In such cases, the milling fluid may be a hydrogen donor such as tetralin or dihydrophenathrene. In some cases, the hydrogen donor may be a gas dissolved in the milling fluid (e.g., gas comprising hydrogen species, or hydrogen). Such processes promote hydrogenation of the coal which may be useful, for example, in producing a liquid hydrocarbon fuel such as gasoline.
It should also be understood that other embodiments of the invention may involve dispersing coal particles after the milling process in any of the “milling” fluids described above. In these embodiments, the fluid used in the milling process may be a conventional milling fluid such as water, or other inert milling fluids.
In certain embodiments, the milling step may occur at temperatures above room temperature (e.g., greater than 30° C.). In some cases, the temperatures may be up to about 300° C. At elevated temperatures, reactions between coal and other components (e.g., milling fluid) may be enhanced. In certain processes, these high temperatures promote separation (e.g., by vaporization) of coal molecules which can be collected. Such molecules may be used, for example, in fuel or non-fuel uses.
In some embodiments, the milling step may occur at temperatures below room temperatures (e.g., less than 15° C.). Lower temperatures may be advantageous in collecting certain components that are separated from coal (e.g., in separation processes) that may have glass transition temperatures above that of the milling temperature, but below room temperature. Such molecules may be used, for example, in fuel or non-fuel uses.
In some methods, swelling agents may be added to the coal particles during, or after, the milling step. Suitable swelling agents are known to those of skill in the art. The swelling agents may cause the coal particles to swell in size, for example, by increasing particle porosity. The increased porosity can enable reactive species within the coal to escape from the coal particle prior to reaction completion and, thus, increasing the amount of reaction taking place external of the particle which may be advantageous.
The above-described small particle sizes and high surface areas lead to a number of advantages that may be found in coal particle compositions of the present invention. For example, the small particles sizes and high surface areas may significantly enhance the reactivity of the coal compositions. Thus, processes that involve reactions with the coal particles (e.g., combustion, extraction, etc.) can be accelerated. This can improve and/or simplify and/or reduce cost of certain existing coal processes and may enable new processes.
The combustion (i.e., burning) efficiency may be substantially increased using coal particle compositions of the present invention. For example, the small particles and high surface areas can lead to rapid combustion which may be nearly instantaneous. This can enhance performance of coal in fuel applications and, in particular, when coal is dispersed in a fluid to form a mixture (e.g., slurry) which can be used as a fuel. Such slurries may also include high solid loadings (e.g., greater than or equal to about 50%) because of the small particle sizes. Suitable fluids may be water, other liquid fuels (e.g., hydrocarbon fuels such as gasoline) oil, or even gas (e.g., air, argon). In particular, coal particles at larger particle sizes typically cannot be effectively transferred using gas (e.g., air); however, the very small particle sizes of coal compositions of the present invention may enable transfer in a gas (e.g., through a powder bed).
Also, the coal particles of the present invention having small particle sizes and high surface areas may enhance separation processes (such as fractional distillation). Such processes liberate molecules from coal which can be used in a variety of applications including fuels (e.g., gasoline), pharmaceuticals, specialty chemicals, plastics and oils. In particular, at the very small dimensions described above (e.g., less than 1000 nm, 500 nm or 100 nm), separation processes may be utilized to obtain specific relatively low molecular weight molecular components (i.e., fractions) which can be particularly valuable in the above-noted applications and which may not be as readily obtained in other conventional processes. The small particles can also lead to substantial cost reductions in separation processes.
The milling process, itself, may be used as a separation process. For example, coal feed particles may be milled to the small dimensions noted above which can lead directly to the separation of coal-based molecules from the feed particles. Such separation may be enhanced by the presence of certain agents and/or heat, though such agents and/or heat are not required. The coal-based molecules may be collected and used in a variety of fuel and non-fuel-based applications as described further below. Such separation may be quantified by measuring the total weight of the coal feed particle composition before and after separation. The difference in the weight is generally due to the separation of coal-based molecules from the coal feed particles. In some embodiments, the separated coal molecules having a total weight of greater than 25% the weight of the coal feed particle composition. In other embodiments, the separated coal molecules have a total weight of greater than 50%, 70%, or even 90% the weight of the coal feed particle composition. The actual degree of separation, may depend on the specific process conditions and particle size of the milled coal particles.
For example, raw coal typically contains pure coal material and non-coal material. The non-coal material may include, for example, pyrite, other aluminosilicate materials, sulfur-containing materials including sulfides, sulfates, organic sulfur, inorganic sulfur (e.g., pyrite sulfur, sulfate sulfur, and the like), minerals such as clays, carbonates, quartz, biotite, rutile, feldspars, hemetite, and various non-combustible ash-forming impurities. The presence of large amounts of these non-coal materials can create problems during combustion. For example, sulfur-containing materials the present in the coal may produce sulfur dioxide when burned. Some methods of the invention may separate the pure coal material from the non-coal material, producing a relatively clean coal product and reducing the production of excessive pollutants.
In some methods, it may even be possible to separate coal molecules from coal particles at low temperatures including less than 100° C., less than 50° C., or even at about room temperature (e.g., about 30° C.). Such temperature ranges may be used to obtain the above-noted weight percentage. Certain prior art techniques, which do not involve milling (e.g., Low Temperature Carbonization, chemical processes using gases such as hydrogen, nitrogen, chlorine, steam, air, and the like, or with solutions such as sodium hydroxide, ferric sulfate, cupric sulfate, and the like), for obtaining such molecules were conducted at significantly higher temperatures (e.g., greater than 400° C.). The milling processes described herein enable separation of certain molecules because of the ability to reduce particle size to such small values (e.g., less than 250 nm, less than 100 nm).
In some embodiments, the milling process may be a reactive milling process. For example, a chemical reaction between the coal particles and the milling fluid may occur during the milling process to form a desired product (e.g., a fuel). In some cases, the coal particles are milled with a milling fluid capable of reacting with the coal feed particles at elevated temperatures (e.g., greater than about 100° C., greater than about 300° C.). The milled coal particles can react with the milling fluid and/or with another chemical species within the fluid (e.g., a gas bubbled through the milling fluid).
The small coal particles may enable equipment advantages. Coal water slurries may be used in systems for electricity generation significantly smaller and less complex than certain conventional systems. For example, small coal particle compositions having low levels of pollution can limit, or even eliminate, the need for scrubbers which otherwise would be used to reduce pollution levels. Smaller coal particles also may lead to less abrasion to equipment that may further process such coal particles (e.g., motors).
Because of the ability of milling processes of the invention to produce very small particles, it may be possible to use coal “fines”, which are a waste product in certain conventional coal processes, as the feed material. Such fines may have an average particle size between 30 and 100 microns and generally have not been used as feed material in typical conventional milling processes. By utilizing a waste product, thus, processes of the invention may have a positive environmental impact.
Coal particles of the invention may be used in a variety of applications including fuel and non-fuel-based applications. The non-fuel based applications include, but are not limited to, additives to other materials (e.g., such as modifiers/fillers in polymeric materials) and use in separation processes to produce components used to synthesize polymeric materials, pharmaceuticals, specialty chemicals, and oils. It should also be understood that coal particle compositions of the present invention may have a variety of other uses beyond those described herein.
Coal particles of the invention may be further processed for certain applications. For example, the coal particles of the invention may be processed to form coal films. In some cases, the films may be very thin (e.g., less than 10 micron, less than 1 micron, or less than 100 nm) because of the very small coal particle sizes obtainable using methods of the invention. In some cases, coal films may even be used as molecular thin films. Coal films may be used in electronic applications as semiconductor layers, conductive layers or shielding layers (e.g., electromagnetic shielding).
The coal particles described herein may also have excellent electrostatic properties and may be used in applications that utilize such properties. For example, the coal particles may be used in electrostatic printing applications (e.g., laser printers, copiers). The small particles sizes obtainable using the methods described herein are particularly important in such applications. In these applications, the coal particles may have an average particle size of less than 1 micron and, in some applications, between about 1 nm and 50 nm. Because of differences between the properties (e.g., triboelectric properties) of coal and other materials used in these applications such as carbon, it is possible to design printing equipment that is compatible with coal particles but incompatible with other types of carbon particles. This enables a manufacturer of printer equipment (e.g., printer cartridges) to limit “after market” sales of such equipment to that which is compatible with coal which may give such manufacturers a competitive advantage.
Coal particles described herein may also be used in ink and dye applications. For example, the coal particles may be used in inks for ink-jet printers and dye formulations for inks.
The following example is meant to be illustrative of certain embodiments of the invention and are not meant to be limiting.

EXAMPLE 1

This example illustrates production of a coal particle composition having an extremely small particle size.
Anthracite coal particles having an average particle size of about 50 microns was used as the feed material. The coal particles were mixed with water to form a slurry which was introduced into a 1.5 inch diameter stirred media mill with 1.8 mm diameter zirconia beads as the grinding media. The particles were milled for about 20 minutes at 3,000 rpm to obtain a coal particle composition having an average particle size of about 10 microns.
The slurry was introduced into a 3 inch diameter stirred media mill with grinding media having a tungsten-titanium carbide composition (i.e., (W:Ti)C including about 10% by weight W) with a density of 16 grams per cubic centimeter. The grinding media had an average particle size between 75 micron and 125 micron. The particles were milled for 1 hour at 2,200 RPM to produce a milled coal particle composition having an average particle size of about 160 nm.
A sample of the slurry of coal and water was collected by evaporating the water at room temperature until the sample was dried. The weight of the dried sample was measured and compared to the weight of the wet sample prior to drying. The measurements indicated that 81 wt % of the coal mass evaporated along with the water. This mass is attributed to the mass of coal molecular species separated from the coal particles during milling. FIG. 1 is a micrograph of representative milled coal particles obtained using SEM analysis.
This example establishes that coal particle compositions having an extremely small particle size can be produced and that coal molecules may be effectively separated from each other at such small particles sizes with substantial amounts of separation being obtainable even at low temperatures (e.g., less than 100° C.).
Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. A coal composition comprising:

coal particles having an average particle size of less than 1.0 micron.

2. A coal composition comprising:

coal particles having an average surface area of greater than 5 m²/g.

3. The composition of claim 1, wherein the average particle size is less than 100 nm.

4. The composition of claim 1, wherein the average particle size is less than 10 nm.

5. The composition of claim 1, wherein the average particle size is greater than 1 nm.

6. The composition of claim 1, wherein a D₉₀value for the composition is less than 250 nm.

7. The composition of claim 1, wherein a D₉₀value for the composition is less than 50 nm.

8. The composition of claim 1, wherein the average surface area is greater than 15 m²/g.

9. The composition of claim 1, wherein the average surface area is greater than 50 m²/g.

10. The composition of claim 1, wherein the average surface area is less than 3,000 m²/g.

11. The composition of claim 1, wherein the coal particles are milled.

12. The composition of claim 1, wherein the coal particles include more than one faceted surface.

13. The composition of claim 1, wherein the particles are substantially spherical.

14. The composition of claim 1, further comprising a fluid in which the coal particles are mixed.

15. The composition of claim 14, wherein the fluid is water.

16. The composition of claim 14, wherein the fluid is oil.

17. The composition of claim 14, wherein the fluid is a gas.

18. The composition of claim 14, wherein the fluid is a fuel.

19. The composition of claim 1, wherein the composition includes less than 0.1% by weight of physical impurities.

20. The composition of claim 1, wherein the composition includes less than 0.1% by weight of chemical impurities.

21. A method of producing a coal composition comprising:

milling coal feed particles to form a milled coal particle composition having an average particle size of less than 1.0 micron.

22. The method of claim 21, comprising milling coal feed particles to form a milled coal particle composition having an average particle size of less than 100 nm.

23. The method of claim 21, wherein the average particle size is less than 10 nm.

24. The method of claim 21, wherein the average particle size is greater than 1 nm.

25. The method of claim 21, comprising milling coal feed particles to form a milled coal particle composition having an average surface area of greater than 15 m²/g.

26. The method of claim 21, comprising milling coal feed particles to form a milled coal particle composition having an average surface area of greater than 50 m²/g.

27. The method of claim 21, wherein the average surface area is less than 3,000 m²/g.

28. The method of claim 21, comprising milling the coal feed particles using grinding media having a density of greater than 8 grams/cm³.

29. The method of claim 21, comprising milling the coal feed particles using grinding media having a density of greater than 10 grams/cm³.

30. The method of claim 21, comprising milling the coal feed particles using grinding media having a density of greater than 15 grams/cm³.

31. The method of claim 21, comprising milling the coal feed particles using grinding media comprising a metal carbide.

32. The method of claim 21, comprising milling the coal feed particles using grinding media comprising a multi-carbide material.

33. The method of claim 21, comprising milling the coal feed particles using grinding media comprising a ferro-tungsten material.

34. The method of claim 21, comprising milling the coal feed particles using grinding media comprising a carburized ferro-tungsten material.

35. The method of claim 21, comprising milling the coal feed particles using grinding media having an average size of less than about 150 microns.

36. The method of claim 21, further comprising removing impurities from the milled coal particle composition by physical separation.

37. The method of claim 21, comprising milling the coal feed particles in a milling fluid capable of reacting with the coal feed particles.

38. The method of claim 37, wherein the milling fluid reacts with the coal feed particles to form fuel.

39. The method of claim 37, wherein the milling fluid reacts with the coal feed particles at a temperature greater than 100° C.

40. The method of claim 37, wherein the milling fluid reacts with the coal feed particles at a temperature greater than 300° C.

41. The method of claim 21, comprising milling the coal feed particles in a milling fluid comprising a light cycle oil (LCO).

42. The method of claim 21, comprising milling the coal feed particles in a milling fluid comprising a hydrocarbon fuel.

43. The method of claim 21, comprising milling the coal feed particles in a milling fluid comprising petroleum.

44. The method of claim 21, comprising milling the coal feed particles in a milling fluid comprising a hydrogen donor.

45. The method of claim 21, further comprising processing the milled coal particle composition in a fractional process.

46. The method of claim 21, further comprising mixing the milled coal particle composition in a liquid.

47. A method of producing a coal composition comprising:

milling a coal feed particle composition to form a milled coal particle composition from the coal feed particles; and

separating coal molecules from the milled coal particle composition at a temperature of less than 100° C., the separated coal molecules having a total weight of greater than 25% the weight of the coal feed particle composition.

48. The method of claim 47, wherein the separated coal molecules have a total weight of greater than 90% the weight of the coal feed particle composition.

49. The method of claim 47, further comprising collecting the molecular separated coal molecules.

50. The method of claim 47, comprising separating coal molecules from the milled coal particle composition at a temperature of less than 50° C.

51. The method of claim 47, separating coal molecules from the milled coal particle composition at about room temperature.