Patent Application
20140223882
The subject matter disclosed herein relates to coal beneficiation and, more specifically, to the separation of ash from the coal in a coal gasification system.
Synthesis gas, or syngas, is a mixture of hydrogen (H2) and carbon monoxide (CO) that can be produced from carbonaceous fuels. Syngas can be used directly as a source of energy (e.g., in combustion turbines), or can be used as a source of starting materials for the production of other useful chemicals (e.g., methanol, formaldehyde, acetic acid). Syngas is produced in large scale by gasification systems, which include a gasification reactor or gasifier that subjects a carbonaceous fuel, such as coal, and other reactants to certain conditions to produce an untreated or raw syngas. To increase the efficiency of the gasification reaction, the ratio of combustible molecules derived from coal to non-combustible scrap, such as ash, within the gasifier is typically maintained within a desired range.
Coal may be collected from various sources, which can lead to different ranks, or qualities, of the coal. Generally, low-rank coals will have higher ash content, while high-rank coking coals have lower ash content. Unfortunately, some geographic sources of coal only extract low-rank coal that may reduce the ability to produce syngas using a typical set of conditions for coal of different or higher rank. As a result, these low-rank coals are particularly problematic and difficult to use, yet their availability would be particularly useful if the ash could be separated from the coal in a simple and cost effective manner. Through the systems and methods described below, low-rank coal may be beneficiated so that it may be used where currently only high-rank coal is being used. Such applications include gasification of coal into syngas, or burning the coal to produce thermal energy. In instances where the coal is not gasified, the beneficiated coal resulting from the processes described below may be used in applications that currently use coking coal.
Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.
In one embodiment, a system includes a feed preparation system, with a fluid injection system configured to inject a fluid into a feed stream to generate a feed-fluid mixture. The feed stream includes a first solid, a second solid, and a gas. The feed preparation system also includes a cyclone configured to separate the feed-fluid mixture into a first stream that includes the first solid and the gas, and a second stream that includes the second solid and the fluid.
In a second embodiment, a system includes a coal beneficiation system that includes a conduit configured to convey coal particles, ash particles, and a conveyance gas. Furthermore, the coal beneficiation system includes a fluid sprayer configured to spray droplets of fluid onto the coal particles and ash particles being conveyed in the conduit and a cyclone configured to generate a coal stream that includes the coal particles and the conveyance gas, and an ash stream that includes the ash particles.
In a third embodiment, a method includes conveying coal particles, ash particles, and a conveyance gas in a conduit, spraying fluid droplets onto the coal particles and ash particles using a fluid sprayer, and generating using a cyclone a coal stream that includes the coal particles and the conveyance gas, and an ash stream that includes the ash particles.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
As discussed below, in embodiments where solid fuel used for syngas production includes a low-rank coal, the solid fuel (i.e., coal) may have unsuitably high amounts of ash, and may have anisotropic concentrations of carbonaceous fuel. This can lead to large temperature variations or other variations within a gasifier and associated equipment, which calls for robust process control systems. To reduce variations such as these, the present embodiments are generally directed toward a dry beneficiation vessel, such as a cyclone, which is configured to deliver a high-rank, consistent feed of a solid fuel, such as coal. The cyclone, in certain embodiments, may include a sprayer that is configured to increase separation of the ash and the solid carbonaceous fuel by increasing the mass differences between the ash and the fuel within the vessel.
The carbonaceous fuel source 18, such as a solid coal feed, may be utilized as a source of energy and/or for the production of syngas or substitute natural gas (SNG). In some embodiments, the fuel source 18 may include coal, petroleum coke, biomass, wood-based materials, agricultural wastes, tars, coke oven gas, asphalt, or other carbon-containing materials. The solid fuel of the fuel source 18 may be passed to the feedstock preparation system 12. The feedstock preparation system 12 may include several subsystems. For example, the feedstock preparation system 12 may perform resizing 28 or dry mixing 30 of the fuel source 18. Resizing, as done by the feedstock preparation system 12 may include, by way of example, use of a grinder, chopper, mill, shredder, pulverizer, or other feature for resizing or reshaping the fuel source 18 by chopping, milling, shredding, briquetting, pelletizing, pulverizing, or atomizing the fuel source 18 to generate feedstock. In the current embodiment, resizing creates the fuel mixture 20, which is typically fine or ultra-fine (e.g., less than about 1 mm) for gasification in the gasification system 16. As defined herein, dry mixing 30 includes processes in which a solid, such as a solid fuel (e.g., coal) is agitated without adding a substantial amount of moisture. Dry mixing adds air or other gases (e.g., inert gases) to the fuel mixture 20, and may be accomplished using gas flows that are substantially free of moisture, or using mechanical agitation features, such as a screw conveyor. As defined herein, substantially free of moisture denotes mixtures, such as gaseous mixtures, which include approximately 5 to 10 percent or less of water or water vapor. As an example, dry mixing with gas may include dry mixing using air, nitrogen, carbon dioxide, helium (He), argon (Ar), neon (Ne), or any combination thereof. Dry mixing also stirs up the fuel mixture 20, which prevents channeling and disperses the particles as they travel to the coal beneficiation system 14. In accordance with present embodiments, no fluid (e.g., water, steam) is added to the fuel source 18 in the feedstock preparation system 12, thus yielding dry feedstock.
The coal beneficiation system 14 includes a cyclone 32, which takes advantage of the differences in mass and density between materials to separate them. As described below, the cyclone 32 separates the fuel dust 22 from the waste 24 by ejecting the lighter material out of the top of the cyclone 32 and allowing the heavier material to drop out of the bottom of the cyclone 32. In embodiments described below, the lighter material is typically the fuel dust 22 while the waste 24 is heavier, and thus drops out of the bottom of the cyclone 32. In previous gasification systems, the high amount of waste 24 contained in some coal types prevented the coal from being used in syngas generation systems 10. The separation methods outlined below, allow a wider variety of coal types to be used as the fuel source 18 in the syngas generation system 10.
As noted above, the flow of fuel dust 22 is provided to the gasification system 16, such as a gasifier, wherein the gasifier may convert the solid fuel into a combination of CO and H2, i.e., syngas. This conversion may be accomplished by subjecting the solid fuel to a controlled amount of steam and oxygen at elevated pressures, e.g., from approximately 20 bar to 85 bar, and temperatures, e.g., approximately 700° C. to 1600° C., depending on the type of gasifier utilized. The gasification process may also include the solid fuel undergoing a pyrolysis process, whereby the feedstock is heated. Temperatures inside the gasification system 16 may range from approximately 150° C. to 700° C. during the pyrolysis process, depending on the fuel source 18 utilized to generate the flow of the fuel dust 22. The heating of the feedstock during the pyrolysis process may generate a solid, e.g., char, and residue gases, e.g., CO, H2, and N2. A partial oxidation process may then occur in the gasification system 16. To aid with this partial oxidization process, a stream of oxygen may be supplied to the gasification system 16. The temperatures during the partial oxidization process may range from approximately 700° C. to 1600° C. Next, steam may be introduced in a controlled amount into the gasification system 16 during a gasification step. The char may react with the CO2 and steam to produce CO and H2 at temperatures ranging from approximately 800° C. to 1100° C. In essence, the system utilizes steam and oxygen to allow some of the feedstock to be partially oxidized to produce CO2 and energy, thus driving a main reaction that converts further feedstock to H2 and additional CO.
For ultra-fine dust like that used in the current embodiment, the accuracy of the cyclone 32 can decrease due to the small differences in mass between the particles. This is especially true when the differences in density are small to begin with. To increase the differences in mass between the waste 24 and the fuel dust 22, the coal beneficiation system 14 may also include a sprayer 50 and a heater 52. The sprayer 50 includes a nozzle 54 that delivers a fluid 56, such as water, steam, saturated steam, oil, or other liquids or gases into the conduit 58 along which the fuel mixture 20 is traveling.
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Technical effects of the invention include the preparation of a fuel source 18 into a fuel mixture 20. The fuel mixture 20 is typically reduced to fine or ultra-fine particles of carbonaceous fuel dust and noncarbonaceous waste. The disclosed embodiments also include the beneficiation of the fuel mixture 20 into the fuel dust 22 and the waste 24. Beneficiation is accomplished using the cyclone separator 32 to separate the dusts based on the difference in mass. Coal beneficiation systems disclosed may include the fluid sprayer 50 and the heater 52 to magnify the physical and chemical differences between the carbonaceous and noncarbonaceous particles. The syngas generation system 10 described in the disclosed embodiments also allows for the gasification of the carbonaceous fuel dust into syngas. The syngas generation system 10 may be included within an IGCC power plant.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
