Patent Application
20130074396
The present invention relates generally to a nano-dispersion of carbonaceous material, such as coal, asphaltite, or the like, in water that is essentially a pseudo-fluid, and optionally other additives. The present invention also relates to the methods of making the nano-dispersion of carbonaceous material in water, which can be used in several applications such as a fuel in boilers, secondary fuel for re-burning applications, as a feed for gasification and Oxycoal units, coal cleaning processes, diesel engines, gas turbines and fuel cells. The nano-dispersion of carbonaceous material in water can also contain another water-soluble fuel such as methanol, ethanol, propanol, butanol and glycerol. An organic immiscible phase, such as spent oil engine or lube oil, hydrocarbons as heavy crude oils and bitumen, diesel, biodiesel, petroleum coke and/or biomass, can also be incorporated into the water in the form of nanodroplets or nanoparticles that enhance carbonaceous material heat of combustion.
Coal comprises a mixture of hydrocarbons and carbohydrates, with small amounts of nitrogen, sulfur, water, and minerals. Coal burns in air with a yellow, smoky flame, leaving ash behind. The energy content of coal depends upon its type. The heat of combustion of brown coal or lignite, for example, is about twenty-five kJ/g, and the heat of combustion of bituminous coal and anthracite is about thirty-two kJ/g. When coal burns, it mainly produces water and carbon dioxide, however it also produces harmful sulfur dioxide, carbon monoxide, hydrocarbons, particulate matter and soot, and oxides of nitrogen (hereinafter “NOx”).
Coal is also the cheapest and most abundant fuel on the world. As a consequence, any technology that allows the use of coal in a cleaner way is necessarily very attractive. Clean coal technologies require, among other things, more reactive coal in order to reduce or eliminate particulate matter and soot, carbon monoxide, hydrocarbons and NOx's emissions. More reactive coal implies complete combustion of coal particles and improved access to reactants or adsorbants to coal surface.
One study that was conducted by Davis et al., uses advanced calculations demonstrating that only coal particle sized below eighteen microns, will burn completely inside a 900 MW tangentially fired boiler retrofitted with low NOx burners (Davis et al., “Evaluating the Effects of Low-NOx Retrofits on Caron in Ash Level”, Reaction Engineering International; Presented at the Mega Symposium: EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium in Atlanta, Ga., August, 1999). It is important to note, however, that currently commercial pulverized coal is typically ground to sixty micrometer average diameter. Further, commercial micronized coal has about fifteen microns average particle size, which means that a significant portion of the particles sizes are above the eighteen micron size, therefore contributing to the carbon in ash content. The Davis et al. study in view of the present invention is incorporated herein by reference.
Decreasing coal particle size implies increasing specific surface area, thereby increasing reactivity. Reducing particle size and obtaining a more reactive coal, opens many other applications, namely, as a feedstock for conventional but less polluting boilers; as a reburn fuel to reduce NOx emissions; as a feedstock of gasification and Oxycoal units; and as a feed in diesel and gas turbines. Further, coal cleaning processes are greatly enhanced by increasing specific surface area, facilitating the extraction of polluting minerals and solid compounds. Hereafter follows a description of these applications and the way they would benefit by using a micronized coal.
Boilers are closed vessels in which water or other fluids are heated. The heated or vaporized fluids exit the boiler for use in various processes or heating applications. In particular, utility boilers, which are typical drum-type boilers, are widely used in power plants, oil refineries, and petrochemical plants for steam generation to drive large turbines, producing electricity. In many instances, these boilers are coal-fired using coal at the burner to produce heated gases used to heat water, thereby generating steam.
Several decades ago, large utility boilers were fitted with pulverized-coal burners designed to fire pulverized coal using about fifteen percent to about twenty percent excess air. Under such conditions, the amount of unburned fuel normally was below two percent, although NOx levels generated by such burners reached levels that are now unacceptable according to current emission standards. In order to meet the current emission standards, low NOx burners have been developed and most commercial coal-fired boilers have been retrofitted with these low NOx burners. Low NOx burners operate to minimize NOx formation by introducing coal and its associated combustion air into a boiler such that initial combustion occurs in a manner that promotes rapid coal devolatilization in a fuel-rich (i.e., oxygen deficient) environment and introduces additional air to achieve a final fuel-lean (i.e., oxygen rich) environment to complete the combustion process. Using these low NOx burners reduces the NOx emissions up to about fifty to about sixty percent.
An example of a low NOx combustion system, such as a boiler with a low NOx burner, available from GE Power Systems is illustrated in
However, the use of low NOx burners increases the carbon content, or unburned coal, in the boiler ash.
The disposal of boiler ash with increased carbon content is becoming a pressing issue within the power utilities markets and will continue to be more so in the future, as the cost of coal and other fuels continue to rise.
One method of utilizing coal as a fuel for utility burners is to create a slurry or dispersion of the coal. For example, the coal is pulverized and mixed with an amount of water in order to form a dispersion or slurry of coal in water at a low enough viscosity so as to enable transportation of the fuel via pipeline or the like. However, because the pulverized or micronized coal is only available at the particle sizes described above, the pulverized coal does not completely burn, and therefore the coal in water slurry does not solve the issues of high carbon content in boiler ash as described above.
Gas turbines can also utilize coal as fuel. A gas turbine is a rotary machine, similar in principle to a steam turbine. It consists of three main components—a compressor, a combustion chamber and a turbine. Air, after being compressed into the compressor, is heated either by directly burning fuel in it or by burning fuel externally in a heat exchanger. The heated air, with or without combustion products, is expanded in a turbine resulting in work output, a substantial part of which is used to drive the compressor. The excess is available as useful work output. In one example, a gas turbine has an upstream air compressor mechanically coupled to a downstream turbine, with a combustion chamber positioned in between. Energy is released when compressed air is mixed with fuel, such as coal, which is then ignited in the combustion chamber. The resulting gases are directed over the turbine's blades, spinning the turbine, and mechanically powering the compressor. Finally, the gases can be passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, electrical generators, and even tanks.
However, commercially available coal-in-water slurries are not conducive to gas turbine applications. When the pulverized or micronized coal is combined with the compressed air and burned, the presence of unburned coal particles can damage the turbine blades, resulting in a less efficient process, and significant expense in replacing the turbine blades.
In diesel engines, a diesel engine relies upon compression ignition to burn its fuel. If air is compressed to a high degree, its temperature will increase to a point where fuel will burn upon contact. Following intake, the cylinder is sealed and the air charge is highly compressed to heat it to the temperature required for ignition. As the piston approaches top dead centre (TDC), fuel oil is injected into the cylinder at high pressure, causing the fuel charge to be nebulized. Owing to the high air temperature in the cylinder, ignition instantly occurs, causing a rapid and considerable increase in cylinder temperature and pressure. The piston is driven downward with great force, pushing on the connecting rod and turning the crankshaft. If commercially available coal-in-water slurries are used as the fuel, the presence of unburned coal particles after combustion of these fuels can cause damage to the cylinders, such as damaging the tolerances between the piston and the cylinder. This in turn may cause damage or failure to the seal of the cylinder, resulting in a lack of pressure to increase the temperature to ignite the fuel, for example.
Coal can also be used as a combustion fuel for a gasification process. Gasification is a process that converts carbonaceous materials, such as coal, petroleum, or biomass, into carbon monoxide and hydrogen by reacting the raw material at high temperatures with a controlled amount of oxygen. The resulting gas mixture is known as synthesis gas or syngas, which can in turn be used as a fuel. The syngas product can be burned directly as a fuel in internal combustion engine, processed into high-purity hydrogen, ammonia, methanol, and other chemicals, or converted via the Fischer-Tropsch process into synthetic fuel. However, commercially available coal-in-water slurries produce a lower quality or contaminated syngas because of the presence of unburned coal particles, as well as clogging of the particulates in the input stream. One example of a gasification process is the Texaco Gasification Process entitled “EPA: Site Technology Capsule—Texaco Gasification Process” having reference EPA 540/R-94/514a of April 1995, which is incorporated herein by reference.
There remains a need for a “green” carbonaceous material to be used as in a carbonaceous material-in-water slurry as a fuel for multiple applications including low NOx burners, gasification processes, gas turbine applications, diesel engine applications, and the like. Such “green” carbonaceous material should completely burn, leaving no particulates in the downstream ash, products, and/or byproducts.
The present invention overcomes the above-described deficiencies. In one embodiment of the invention, a nano-dispersion of carbonaceous material in water creates a relevant colloidal fraction slurry that can include from about fifty to about eighty weight percent, and more particularly about sixty to about seventy weight percent of carbonaceous material. In one embodiment of the invention, the carbonaceous material slurry has a relatively narrow particle size distribution with virtually no particles above 100 microns, about forty percent of the carbonaceous material having a particle size of at least less than ten microns, and at least ten percent of the carbonaceous material having a particle size of one micron or less. The total carbonaceous material content of this kind of relatively narrow particle size distribution has an upper limit of sixty to sixty two weight percent and the viscosity of the carbonaceous material slurry is about 1000 centipoise (cP) or less at 120 degrees Fahrenheit.
Carbonaceous materials can include, for example one or more combinations including spent oil engine, hydrocarbons as heavy crude oils and bitumens such as asphaltite, diesel, petroleum coke, biodiesel, biomass, and coal such as, but not limited to, lignite, bituminous coal, anthracite, as describe in U.S. Patent Application Publication No. 2010/0024282 to Joseph et al., incorporated herein by reference in its entirety. In one particular embodiment, the carbonaceous material comprises asphaltite including gilsonite (uintaite), glance pitch, and grahamite.
In another embodiment of the invention, the heat derating can be decreased significantly by increasing the carbonaceous material content up to seventy to seventy two weight percent. This can be achieved, for example, in the case of coal, by combining the relevant colloidal fraction coal slurry with dry large coal particles or slurry of large coal particles that can be at least one hundred times larger than the colloidal coal particles. By this means, coal content may be increased up to seventy to seventy two weight percent with virtually no increase in slurry viscosity creating a pseudo-fluid. The mass fraction of the large particle size coal is about 25 to 35% of the total coal in the slurry.
In another embodiment of the invention, the heat of combustion can also be increased by adding to the carbonaceous material in water slurry a volatile or water-soluble fuel such as methanol, ethanol, propanol, butanol and glycerol. The component can also be an organic immiscible phase such as spent oil engine, hydrocarbons as heavy crude oils and bitumens such as asphaltite including gilsonite (uintaite), glance pitch, and grahamite, diesel, petroleum coke, biodiesel and biomass. The organic immiscible phase is preferably dispersed into nanodroplets or nanoparticles that enhance the heat of combustion of the carbonaceous material(s).
In another embodiment of the invention, the carbonaceous material slurry also includes from about 500 to about 3000 ppm of one or more surfactants and/or an inorganic or organic salt, and/or light and/or heavy alcohols. The surfactants can be ionic or nonionic. The nonionic surfactants can include, for example, primary or secondary ethoxylated alcohols with two to thirty ethoxylate oxide molecules, or ethoxylated nonylphenols with two to thirty ethoxylate oxide molecules. The ionic surfactants can include sodium alkyl sulfates, sodium alkyl sulfonates, alpha olefin sulfonates, alpha olefin sulfates, alkyl benzene sulfonates, sodium sulphosuccinates, sodium lauryl ether sulphate, quaternary ammonium chloride, bromide, or imidazolines or betaines. The inorganic and organic salt cations can include sodium, calcium, or magnesium.
In yet another embodiment of the invention, a method for preparing a carbonaceous material in water slurry includes optionally mixing the components in the presence of one or more of the aforementioned chemical additives. The water phase may contain miscible and volatile components such as methanol, ethanol, propanol, butanol and glycerol or inmiscible oil nanodroplets or nanoparticles from biomass. The slurry is mixed in a chamber with a slit channel that spins a film of the slurry components and creates a centrifugal field in excess of thirteen thousand gs. Stagnation regions in the mixing flow field concentrate the carbonaceous material, and then mill it in a wet-communication process. Cooling agents, in order to maintain water temperature below evaporation, control the mixing temperature.
In another embodiment, the carbonaceous material in water slurries having nano-dispersions of carbonaceous material can be used in low NOx burners as a main fuel, reburn fuel or both, as fuel in gasification and oxycoal processes, as a fuel in diesel engine applications, and/or as fuel in gas turbine applications and fuel cells.
The above summary of the invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description that follow more particularly exemplify these embodiments.
Nano-dispersions of carbonaceous material-in-water slurries that contain a relevant colloidal fraction according to embodiments of the current invention solve the above-mentioned deficiencies. The carbonaceous material-in-water slurry generally comprises a micron-sized fraction and a colloidal suspension or nano-dispersion of milled particles in water, the particles having a large particle population of sub-micron size. The carbonaceous material-in-water slurry can further comprise a surfactant system that is particularly formulated depending on the type and source of carbonaceous material. The carbonaceous material-in-water slurry can be used as a fuel for not only the reburn and/or main fuel in a low NOx burner, but also has potential applications in gasification processes, gas turbines, and diesel engines. Because of the carbonaceous material's small particle size, and therefore larger surface area compared to commercially available carbonaceous material-in-water slurries, a burning efficiency of the carbonaceous material is near one hundred percent, leaving virtually no carbonaceous material particles in the ash or the resulting gases.
As discussed above, any of a variety of carbonaceous materials can be utilized as an alternative to or in addition to coal. Such carbonaceous materials can include, but are not limited to, spent engine oil, hydrocarbons including allochthonous materials, such as heavy crude oils and natural bitumens and asphalt or asphaltite, diesel, petroleum coke, biodiesel, biomass, and coal such as, but not limited to, lignite, bituminous coal, and anthracite, or combinations thereof. In one particular embodiment, the carbonaceous material comprises one or more soluble natural bitumens (e.g. CS2 soluble) including mineral wax, natural asphalt, and/or asphaltite. More particularly, the soluble natural bitumen comprises one or more asphaltites including gilsonite (uintaite), glance pitch, and grahamite. Asphaltite offers lower sulfur content than conventional coal sources such as lignite, anthracite, or bituminous coal because asphaltite generally contains little or no inorganic materials including sulfur. In one embodiment, an asphaltite in water slurry is substantially free of sulfur, i.e. it contains negligible amounts, such that when used as a fuel, little to no sulfur-containing byproducts, such as sulfur dioxide, are produced.
In one embodiment of the invention, a carbonaceous material-in-water slurry, such as a coal-in-water slurry, comprises from about fifty to about seventy two weight percent of carbonaceous material dispersed in water, and more particularly from about sixty to about seventy weight percent of carbonaceous material. The carbonaceous material can comprise suitable coals to be used as fuel, such as, for example, lignite, sub-bituminous, bituminous, and anthracite. In an alternative embodiment, the carbonaceous material can comprise a natural bitumen, and more particularly asphaltite.
The particle size distribution of the carbonaceous material-in-water slurry can include, for example, a micron-sized fraction having a particle size of about ten microns to about 1 micron and a sub-micron colloidal fraction having a particle size less than about one micron to about 100 nm with an average particle size of the sub-micron colloidal fraction being about 200 nanometers to about 300 nanometers. A person of ordinary skill in the art will recognize that ranges and subranges within these explicit ranges are contemplated and are within the present disclosure. In a preferred embodiment, the sub-micron colloidal fraction has an average particle size of about 250 nanometers. In one embodiment of the present invention, the particle size distribution is bimodal, having one mode with an average particle size of about one micron or less. In an alternative embodiment of the present invention, the particle size distribution is unimodal with a Sauter mean diameter particle size of about five microns or less. A multi-modal particle size distribution of carbonaceous material-in-water slurries according to an embodiment of the invention is shown at
In certain embodiments, the micron and sub-micron colloidal fractions of carbonaceous material, which have a particle size (Sauter mean diameter) of about 10 microns or less, can comprise between about 30 and about 50 weight percent of the carbonaceous material-in-water slurry, with the sub-micron colloidal fraction that has a particle size less than about one micron comprising at least about 20 weight percent to about 85 weight percent of such carbonaceous material having a particle size of about 10 microns or less (Sauter mean diameter). In other aspects, the micron and sub-micron colloidal fractions together comprise about 58 weight percent to about 62 weight percent of the carbonaceous material-in-water slurry.
In one embodiment of the invention, the carbonaceous material-in-water slurry has a viscosity of about 350 to about 1000 centipoise (cP) at 120 degrees Fahrenheit. A person of ordinary skill in the art will recognize that ranges and subranges within these explicit ranges are contemplated and are within the present disclosure. A viscosity at the lower end of this range allows for standard fuel transportation means, such as, for example, pipelining, tanker trucks, and ships and barges. Further, by virtue of the coal's small particle size, the suspension is relatively stable, with very little sedimentation.
In certain embodiments, nano-dispersions of carbonaceous material in water according to the present invention have a maximum amount of dispersed carbonaceous material, which when surpasses causes the nano-dispersion to lose its pseudo-fluid characteristic. This has to do with carbonaceous material particles running out of space in the bulk of the water as more carbonaceous material is added. The upper bound of carbonaceous material content depends on the way particles arrange among themselves which, in turn, depends on the geometry of the entire particle assembly. This non-unique upper bound is known as the maximum packing fraction. When the carbonaceous material content approaches this mass fraction, particle interactions are greatly increased because particles virtually touch each other; once the slurry surpasses the maximum packing fraction, the slurry no longer behaves like a fluid but rather as a wet solid or paste. As a consequence, slurry fluidity diminishes significantly. Besides, colloidal interactions also contribute to paste like behavior. However, modifying particle size distribution, in such a way as to reduce local interactions, can increase the maximum packing fraction. This can be achieved by combining large particles with much smaller particles, at least 100 times smaller. The smaller particles, along with the continuous phase, become a pseudo-continuous fluid to the large particles. The resulting macroscopic effect is a significant reduction of viscosity, as long as the size ratio of large particles to small particles is greater than 100.
In one embodiment of the present invention, about fifty eight to about sixty two weight percent nano-dispersed carbonaceous material in water slurry, as described above, is manufactured followed by the addition of dry large carbonaceous material particles or a concentrated slurry of large carbonaceous material particles, having particles sizes in the range of 150 to 400 μm. A person of ordinary skill in the art will recognize that ranges and subranges within these explicit ranges are contemplated and are within the present disclosure. This procedure gives way to more concentrated carbonaceous material slurry, with about sixty eight to about seventy two weight percent of carbonaceous material, with sub-ranges and values within this range contemplated and present within this disclosure, and a broad particle size distributions, still having a significant colloidal fraction that behaves as a pseudo-fluid to the large particles. Since this pseudo-fluid is more viscous than the continuous phase alone, sedimentation of both the sub-micron and the large particles is virtually eliminated because the relevant colloid fraction creates a viscous pseudo-fluid that suspends the large particles. In other words, the density difference between the carbonaceous material particles and the pseudo-fluid to prevent sedimentation is about less than 10%, preferably less than 5%, and optimally 2% or less. This behavior has an important economic implication. Since the viscous pseudo-fluid prevents sedimentation, there is no need of additional chemical compounds to prevent settling (polymers, for example, that are necessary in conventional slurries) thereby reducing additives cost in a significant way.
Carbonaceous material slurries of the present invention in which the carbonaceous material content is greater than sixty two percent are of interest in gasification and oxy combustion processes. In these applications, boiler temperatures are very high thus allowing complete carbonaceous material burning while gaining thermal efficiency associated with less boiler de-rating owing to the reduced water content in the slurry fuel.
In yet another embodiment of the invention, a volatile water miscible component, that also has combustion properties, can be added to increase heat of combustion. The volatile component can be methanol, ethanol, butanol and glycerol, or a combination thereof. While the optimal amount of volatile component is dependent upon the volatile being added, in certain embodiments the preferred weight percent of the volatile component is less than 10%, and optimally 3-6%. A person of ordinary skill in the art will recognize that ranges and subranges within these explicit ranges are contemplated and are within the present disclosure. Methanol, ethanol and butanol are water soluble and volatile, and they can be obtained as sub-products of biomass fermentation. Biodiesel production from vegetable oils transesterification implies, in some cases, the generation of high volumes of glycerol solutions that can be combined with carbonaceous material to produce a higher heat value for the fuel slurry.
In another embodiment of the invention, the heat of combustion can also be increased by adding to the carbonaceous material water slurry, an organic liquid or oil that is immiscible in water. The organic liquid or oil would also be a nano-dispersion, this is, an oil-in-water nanoemulsion. The organic or oil phase can comprises spent engine oil or lube oil, crude oil and bitumen, diesel and biodiesel or any other hydrocarbon product that is emulsified in the water phase, previous to the preparation of the carbonaceous material slurry. Alternatively, the organic or oil phase can also be combined with the previously prepared carbonaceous material in water suspension. In certain embodiments, the preferred weight percent of the organic liquid or oil component is less than 10%, and optimally 3-6% with other ranges and subranges within these explicit ranges being contemplated and within the present disclosure.
In another embodiment of the invention, adding to a coal in water slurry, finely dispersed solid particles that are combustible, can also increase the heat of combustion. The origin of the combustible solid particles may be hydrocarbons as heavy crude oils and bitumens like asphaltite, diesel, petroleum coke, biodiesel, and/or biomass. The solid dispersion can be the base for the preparation of coal slurry, or the solid particle slurry can be the base for the incorporation of the coal into the slurry. In certain embodiments that contain the finely dispersed solid combustible particles, the nano-dispersion of coal-in-water contains about fifty eight to about sixty two weight percent nano-dispersed coal in water slurry, as described above, with the remaining weight percent of the particles dispersed in water comprising the solid combustible particles of hydrocarbons as heavy crude oils and bitumens like asphaltite, diesel, petroleum coke, biodiesel, biomass, or a combination thereof. A person of ordinary skill in the art will recognize that ranges and subranges within this explicit range are contemplated and are within the present disclosure.
In yet another embodiment of the invention, the carbonaceous material-in-water slurry comprises a surfactant system. For example, not all sources of coal have the same properties, but rather the surface properties of coal can depend on the type and/or source of the coal being used. Therefore, surfactant systems can be carefully tailored to each type and/or source of coal, or other carbonaceous material. Further, if a volatile or combustible component is added to the slurry, the surfactant system has to ensure the dispersability and stability of the carbonaceous material particles in an aqueous phase that may have soluble components (methanol, ethanol, propanol, butanol, glycerol), or oil droplets (spent engine and lube oil, diesel and biodiesel, crude oil or bitumen) or a second type of combustible solid particles (biomass).
A surfactant system according to embodiments of the invention can comprise a single surfactant, a mixture of two or more surfactants, or mixtures of one or more surfactants and an inorganic and/or organic salt, or a mixture of one or more surfactants with amines or light and heavy alcohols. Suitable surfactants can comprise one or more nonionic surfactants and/or one or more ionic surfactants. Nonionic surfactants can include, for example, primary or secondary ethoxylated alcohols having two to thirty ethoxylate oxyde molecules, and/or ethoxylated nonylphenols having two to thirty ethoxylate oxyde molecules. Ionic surfactants can include, for example, sodium alkyl sulfates, sodium alkyl sulfonates, alpha olefin sulfonates, alpha olefin sulfates, alkyl benzene sulfonates, sodium sulphosuccinates, sodium lauryl ether sulphate, quaternary ammonium chloride, quaternary ammonium bromide, imidazolines, betaines, and combinations thereof. Cations of suitable inorganic and organic salts can include, for example, sodium, calcium, and/or magnesium.
In one embodiment of the invention, a surfactant system is present in the carbonaceous material-in water-slurry at about 500 to about 3000 parts per million (ppm). A person of ordinary skill in the art will recognize that ranges and subranges within this explicit range are contemplated and are within the present disclosure. In another embodiment of the present invention, a surfactant system of about up to 1 weight percent is included in the nano-dispersion of carbonaceous material-in-water when the slurry contains at least one volatile component and/or at least one organic liquid or oil component.
A method of making carbonaceous material-in-water slurries is dependent upon the milling technology in order to produce carbonaceous material particles, such as coal particles, in the sub-micron range. In one embodiment of the invention in which the carbonaceous material comprises coal, pulverized or non-pulverized coal, water, and optional surfactant system are combined in a chamber of a suitable mixer, such as, for example, the Filmics Mixer, available from the Primix Corporation of Osaka, Japan. The Filmics Mixer and accompanying technology is set forth in U.S. Pat. No. 5,582,484 entitled “Method Of, and Apparatus For, Agitating Treatment Liquid”, which is incorporated herein by reference. The slurry is mixed in the chamber with a slit channel that spins a film of the slurry components and creates a centrifugal field of about thirteen gs or more. Stagnation regions in the mixing flow field then concentrate the coal and mill the coal in a wet-comminution process, milling the coal into the micron and submicron particles as previously disclosed. In a preferred embodiment, the wet-comminution process is a continuous process with the source of coal having about 3 to about 20 seconds of residence time, optimally about 9 seconds, with other ranges and subranges of these explicit ranges contemplated and within the present disclosure. The formation temperature of the slurry is controlled by cooling agents to maintain the water temperature below evaporation. Coal particles micronized by milling according to commercially standard processes are shown in
This wet-comminution process also offers safety advantages over dry milling. Dry milling coal, such as that done in a Fuller mill, to a micron or submicron size can cause the coal particles to be released into the air. Often times, costly sophisticated systems, such as magnetic fields, are used to control the release of the coal particles. However, the wet-comminution process allows the coal particles to remain suspended in the water, reducing or eliminating the introduction of coal particles into the air.
In yet another embodiment of the invention, if a volatile or combustible component is required to decrease heat derating, which may be an ignition problem with the additional dividend of reduced derating, the slurry preparation may require two mixing steps. In the first step, water is combined with soluble alcohols (i.e., methanol, ethanol and/or butanol) and/or glycerol and then coal and aqueous phase are mixed and processed in the wet-comminution apparatus. Alternatively, the soluble alcohols and/or glycerol are added to the coal slurry after the wet-comminution process. Regarding the combination with an organic or oil phase, or a finely dispersed solid biomass, the wet-comminution process is used to produce a nanoemulsion (organic or oil phase) or nanosuspension (dispersed solid biomass) that is later combined with coal water slurry that has also been produced by the wet-comminution process. In a variant of the present invention, the nanoemulsion is produced by a conventional mixer using a special surfactant package, or by means of the wet-comminution method and the special surfactant package. In yet another alternative embodiment, the wet-comminution process is used to produce first the nanoemulsion or nanosuspension, and then used again to mill the coal into micron and/or submicron size in the nanoemulsion or nanodispersion.
According to one embodiment of the invention, the carbonaceous material-in-water slurry with nano-dispersed particles can be used as the main fuel, the reburn fuel, or both, in a boiler, such as a low NOx boiler. The small particle size of the carbonaceous material particles in the slurry increases the surface area available for firing or burning, as compared to commercially available micronized carbonaceous material-in-water slurry. The increased surface area results in increased flame times twice as long or more compared to commercially available slurries, and virtually complete or clean burning of the slurry and carbonaceous material particles, even in low oxygen atmospheres. A graph comparing the flame times of commercial slurries and the slurries of the present invention is illustrated at
Because of the clean burning characteristics of the nano-dispersion of carbonaceous material-in-water slurry of the present invention, there is virtually no carbonaceous material present in the ash in boiler applications. This clean burning application can therefore reduce the amount of carbonaceous material needed for power generation than the current low NOx burners, producing a savings of upwards of millions of dollars a year on carbonaceous material supplies, such as coal supplies.
In another embodiment of the invention, the carbonaceous material-in-water slurry with nano-dispersed carbonaceous material particles, such as coal, can be used in gasification processes, such as the Texaco Gasification Process previously referenced.
In yet another embodiment of the invention, the carbonaceous material-in-water slurry with nano-dispersed particles can be used in gas turbine applications. For example, methanol, ethanol, glycerol or any other similar fluid hydrocarbon can be added to the slurry to create a water/alcohol or polyalcohol mixture with carbonaceous material particles for a fuel. Because the carbonaceous material burns essentially completely, there are few or no carbonaceous material particles in the resulting gases from the combustion chamber. Therefore, there is a little danger of damaging the turbine blades.
The virtual elimination or mass reduction of carbonaceous material particles in the combustion of the carbonaceous material-in-water slurries of the present invention also allows one to use them as fuels in diesel engines, such as marine diesel engines, independent power producers (IPP) diesel engines, and standard diesel engines. The occurrence of damage to the cylinder and/or piston is greatly reduced due to the clean burning of the particles.
In yet another embodiment of the invention, the carbonaceous material-in-water slurry of the present invention can be used in any application employing a Rankine cycle. The Rankine cycle is a thermodynamic cycle which converts heat into work. The heat is supplied externally to a closed loop, which usually uses water as a working fluid. There are four processes in the Rankine cycle, each changing the state of the working fluid: 1) the working fluid is pumped from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy; 2) the high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor; 3) the dry saturated vapor expands through a turbine, generating power—this decreases the temperature and pressure of the vapor, and some condensation may occur; and 4) the wet vapor then enters a condenser where it is cooled at a constant pressure and temperature to become a saturated liquid—the pressure and temperature of the condenser is fixed by the temperature of the cooling coils as the fluid is undergoing a phase-change. The Rankine cycle describes a model of the operation of steam heat engines most commonly found in power generation plants. However, because of the diesel applications that can be achieved using the carbonaceous material-in-water slurry, the boiler of the Rankine cycle can be replaced with a diesel engine. Alternatively, the carbonaceous material-in-water slurry can be used as the main fuel and/or reburn fuel of the boiler of the Rankine cycle, as discussed above.
In the examples following infra, coal is used as the primary source of carbonaceous material for exemplary purposes only.
Combustion characterization studies were performed comparing colloidal coal-in-water slurries according to embodiments of the current invention to a slurry made with a conventional coal grind. The slurries were used in pilot-scale reburning tests to highlight any performance advantages to using a micronized coal water slurry product in terms of NOx reduction and carbon burnout as a reburn fuel compared with conventional coal water slurry. Nine reburn tests were conducted. Test variables included reburn zone residence time, reburn heat input, and initial NOx concentrations. The complete study is set forth in “NDT Combustion Characterization Studies,” Oct. 27, 2008, which is incorporated herein by reference in its entirety. In the study, the nano-dispersion of coal in water was referred to as “micronized.”
1. Equipment, Slurry Preparation, and Test Parameters
The reburning tests were conducted in a boiler simulation furnace (BSF) test unit that is designed to simulate a coal-fired boiler. The BSF used has a firing rate range of 200,000 to 1,000,000 Btu/hr. The atomization air flow rate was held constant and the air-to-liquid mass ration ranged from approximately 1.0 to 0.5 as reburn heat input varied from about 10-20%.
The conventional coal water slurry used as the reburn fuel for the test included a conventional grind with a size distribution such that approximately 70% of the material passed through a US 200 mesh sieve, typically used in US pulverized coal-fired boilers. The coal used as the base for the conventional coal water slurry is shown in the table below:
The nano-dispersion of coal was prepared according to the wet-comminution method descirbed herein. Particularly, after milling coal in an IKA® mill, particle sizes were, in general evenly distributed from very large to very small sizes, i.e. mostly unimodal or slightly bimodal distributions. According to sieving tests, particle populations below 20 μm increased initially from a concentration of 10-30% to 50-60% w/2 after the wet-communition process. Particles could be as small as 100 nm, depending on the type and content of coal, intial grind and process conditions such as viscosity prior to the wet-comminution, residence time and total energy input. In general, it was found that both low viscosity and high coal content would improve comminution and the best results were obtained for dispersions having coal contents between 55 to 60%. In this range, coal content was sufficiently high and viscosity was still manageable.
Microscopic observations confirmed the sieve results, while measurements with a Nanotrac showed a significant overall reduction in size of the colloidal population (<6.5 μm). Typical sieving results are shown in
Additionally, the graph in
The water content of both the nano-dispersion and the initial conventional coal slurry was 40% by weight. However, it was readily apparent that the conventional slurry had different handling, pumping, and atomization characteristics than the nano-dispersion slurry. Specifically, the conventional slurry with 40% water had poor atomization quality and tended to plug the injection system. Therefore, to qualitatively simulate the handling and atomization characteristics of the nano-dispersion slurry, most conventional slurry reburning tests were performed with slurry containing 45% water. It was observed that even after shipment and storage for several weeks of the nano-dispersion slurry, the slurry did not settle in the containers and maintained good condition. On the other hand, the initial conventional coal slurry with 40% water by weight settled in the bottom of the storage container within a few hours.
Two series of reburning tests were performed, including one with nano-dispersion of coal in water slurry and one with conventional coal water slurry. The slurry was the reburn fuel, with natural gas as the main fuel. After stable emissions were verified during natural gas firing, slurry was pumped and atomized into the BSF furnace zone. NOx emissions were measured throughout the tests to determine the achievable NOx reduction, and for selected test conditions, ash samples were collected from the convective pass of the BSF and loss of ignition (LOI) was measured.
Test variables included reburning heat input ranging from about 10% to about 20% and varied by adjusting the reburn fuel flow rate, reburn zone residence time (240 to 590 ms) varied by moving the overfire air injector position, initial NOx concentration (250 to 400 ppm) varied by adjusting burner conditions, and slurry water content (40% and 45%). The following table set forth the test matrix:
2. Test Results
At high initial NOx concentration (400 ppm) and short reburn zone residence time (240 ms), the reburn performance for micronized slurry is slightly better compared to that of conventional slurry, as illustrated in the graph of
At low initial NOx concentration (250 ppm) and short reburn zone residence time (240 ms), the reburn performance of micronized 40% water slurry is comparable to that of 45% conventional slurry, as illustrated in the graph of
The effect of initial NOx concentration on reburn performance while keeping the same reburn zone residence time (240 ms) was also measured. The reburn performance of 40% water micronized slurry appears to be better compared to that of conventional 45% slurry at 15% and 20% reburn heat input. Reburn performance for micronized and conventional slurry is comparable and within the same range at 10% reburn heat input, as illustrated in the graph of
The effect of reburn zone residence time on reburn performance while keeping same initial NOx concentration (400 ppm) was also measured. The reburn performance of micronized slurry appears to be better compared to that of conventional slurry at 15% and 20% reburn heat input. Reburn performance for both micronized and conventional slurry is comparable and within the same range at 10% reburn heat input, as demonstrated in the graph of
The current coal-water slurry reburning results were also compared in the context of other reburning fuels that have been tested at the BSF. Natural gas is the most reactive of these fuels due to its ability to readily disperse and react. However, natural gas is also typically the most expensive reburning fuel, and thus there is commercial interest in utilizing other fuels such as coal for reburning. The micronized slurry was generated using a bituminous coal that on its own would not be expected to be highly reactive. The results are illustrated in the graph of
Three fly ash samples were collected and measured for loss on ignition (LOI) at 20% reburn heat input for both micronized and conventional slurry to determine if the micronized slurry is different from the conventional slurry in terms of carbon content in ash. The LOI is lightly lower for micronized slurry reburn tests for all test conditions, as illustrated in the graph of
The following table is a summary of all test results, in which it was observed that for all the reburn test conditions, the micronized coal water slurry with 40% water performed better than the conventional coal water slurry with 45% water, and that for all reburn test conditions the micronized coal water with 40% water performed at least as well as, and in some cases better than, the conventional coal water slurry with 45% water. NOx reduction performance of micronized slurry appears to have more advantages at higher reburn heat inputs and longer reburn zone residence times. The values of Loss on Ignition results were slightly lower for reburn tests with micronized slurry than with conventional slurry.
The development of a super green coal to be used as a carbonaceous material-in-water slurry according to embodiments of the invention has the potential of massive savings in the applications as described above, and particularly in the low NOx burner applications because less carbonaceous material is needed to produce the same amount of energy produced in today's applications. Further, the virtually complete burning of the coal reduces the amount of carbonaceous material present in the waste streams, such as the ash of a boiler.
The invention therefore addresses and resolves many of the deficiencies and drawbacks previously identified. The invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive. The claims provided herein are to ensure adequacy of the present application for establishing foreign priority and for no other purpose.
The present application claims the benefit of U.S. Provisional Application No. 61/473,017 filed Apr. 7, 2011, which is incorporated herein in its entirety by reference, and the present application is a continuation-in-part of application Ser. No. 12/495,151 filed Jun. 30, 2009, which claims the benefit of U.S. Provisional Application No. 61/077,009 filed Jun. 30, 2008, and U.S. Provisional Application No. 61/157,089 filed Mar. 3, 2009, each of which is hereby fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61473017 | Apr 2011 | US | |
| 61077009 | Jun 2008 | US | |
| 61157089 | Mar 2009 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12495151 | Jun 2009 | US |
| Child | 13442134 | US |
