Coal gasification process with conversion of CO2 to oxygen gasifier feed producing carbon by-product

Abstract

A process and apparatus for the enhancement of syngas (CO and H.sub.2) to fuels production utilizing a carbon based feedstock, (for example coal) by exploiting some, or all, of the hot CO.sub.2 produced during the gasification step, and converting the CO.sub.2 through electrochemical reactions into oxygen (O.sub.2) and carbon via a molten salt reactor and directing the oxygen back to the gasifier to minimize or eliminate the need for an oxygen plant, while the carbon by-product (granular carbon) will be used for a variety of adsorbents for environmental applications.

Claims

1. A coal gasification process and carbon dioxide conversion process consisting of the steps of producing a raw syngas from a gasifier heating coal producing a syngas product having a temperature of from 800 to 1200 C., said gasification process forming a syngas product containing a carbon dioxide where a gasifier for use in the process is operated over a range of pressure between 15 and 1500 psi and a temperature from 750 to 1200 C.; purifying said syngas product containing said carbon dioxide with a purification unit fluidly coupled to said gasifier; removing said carbon dioxide from said syngas product with a carbon dioxide separation/recovery unit fluidly coupled to said purification unit; compressing said carbon dioxide with a compressor fluidly coupled to said carbon dioxide separation/recovery unit forming a concentrated carbon dioxide product forming a compressed carbon dioxide product; cooling and reducing the temperature of said syngas product with a heat exchanger fluidly coupled to said gasifier; recovering syngas carbon neutral heat energy removed from said syngas product during cooling with said heat exchanger and using said syngas carbon neutral heat energy to drive a conversion/disassociation of said carbon dioxide product into a carbon product and an oxygen product by circulating at least a portion of said syngas carbon neutral heat energy through a molten salt reactor fluidly coupled to said heat exchanger unit and said gasifier by: a) heating said molten salt reactor to a selected temperature utilizing said carbon neutral heat energy generated from said heat exchanger from cooling a least a portion of said syngas product, said carbon neutral heat energy producing at least a portion of the heat necessary to operate said molten salt reactor; b) feeding said compressed carbon dioxide product to said molten salt reactor; and c) converting and disassociating said compressed carbon dioxide product with said molten salt reactor producing carbon by-product collecting on an anode of said molten salt reactor and a pure oxygen product released at a cathode of said molten salt reactor; feeding said pure oxygen product produced in said molten salt reactor to said gasifier; and removing said carbon by-product produced in said molten salt reactor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A better understanding of the present invention will be had upon reference to the following description in conjunction with the accompanying drawings in which like numerals refer to like parts throughout the views wherein:

(2) FIG. 1 illustrates a process flow diagram illustrating the use of a gasifier to produce syngas for a feed to a FT unit; CO.sub.2 will be separated from the syngas. The syngas acts as a heat source and is typically 800-1000 C. depending on the type of gasifier used, (but may be more or less depending upon the selected gasifier) will drive the molten salt reactor, heating the reactor to a constant 500 C. using the CO.sub.2 from the gasifier as feed to produce an oxygen resource that can be fed to the gasifier. An additional carbon product is also generated and can be upgraded to useful sorbents.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(3) The present invention comprises, consists of, and/or consists essentially of a process that includes a series of steps for the gasification of coal and subsequent syngas applications that include: 1) energy (Heat) recovery to drive the conversion/dissociation of CO.sub.2 into C and O.sub.2 and; 2) production of O.sub.2 from CO.sub.2 for the oxygen plant used during gasification.

(4) The process is uses a conventional gasifier such is available from the LURGI company, that generates a desirable syngas with a H.sub.2/CO ratio suitable for FT applications, or any H.sub.2/CO syngas for other non-FT applications (i.e., chemical synthesis etc.). The heat recovery during the cooling of the syngas is a critical energy input (at least part of the energy required) to spilt CO.sub.2 into C and O. The syngas exit temperature from the gasifier is 800 to 1200 C. The syngas has to be cooled and conditioned (cleaned of impurities such as sulfur, CO.sub.2) for the FT process. Separation of the CO.sub.2 is an established technology. The cleaned syngas needs to be cooled and prepared for the FT reactor. This critical cooling step allows for heat recovery using heat exchanger technology to gain CARBON-NEUTRAL ENERGY that will be used to drive the conversion/dissociation of CO.sub.2 into oxygen and carbon. The formation of oxygen from CO.sub.2 conversion is used for the gasification of coal. For example, the recovered heat energy from the syngas will be directed to heat a molten salt reactor. The molten salt reactor electrochemically converts CO.sub.2 to activated carbon and oxygen. The activated carbon is an additional value added product which may be utilized a catalyst or other carbon product. The oxygen will be directed to the oxygen plant and recycled as a required part of the coal gasification process.

(5) Heat recovery may be achieved using heat exchangers, or any other route (electricity generation) to heat the molten salt reactor to a selected temperature, for example 500 C. The molten salt reactor has two electrodes. At the anode high surface area carbon will be deposited and oxygen will be released at the cathode. The molten metal salt reactor is one example to use the recovered carbon-neutral heat energy to dissociate CO.sub.2 to carbon and oxygen.

(6) A better understanding of the invention can be facilitated by a careful consideration of the preferred process outlined in FIG. 1. Coal and/or other combustible hydrocarbonaceous materials, which can include coke, lignite, oil shale, peat, biomass, petroleum refining residues and the like, are charged through conduit 12 to coal gasification unit 14. While the preferred embodiment utilizes coal as a preferred feed product, the carbonaceous materials can include but are not limited to, biomass (e.g., plant and/or animal matter or plant and/or animal derived matter); coal (e.g., high-sodium and low-sodium lignite, lignite, sub-bituminous, and/or anthracite); oil shale; coke; tar; asphaltenes; low ash or no ash polymers; hydrocarbon-based polymeric materials; biomass derived material; or by-product derived from manufacturing operations. The hydrocarbon-based polymeric materials can include, for example, thermoplastics, elastomers, rubbers, including polypropylenes, polyethylenes, polystyrenes, including other polyolefins, homo polymers, copolymers, block copolymers, and blends thereof; PET (polyethylene terephthalate), poly blends, other polyolefins, poly-hydrocarbons containing oxygen; heavy hydrocarbon sludge and bottoms products from petroleum refineries and petrochemical plants such as hydrocarbon waxes, blends thereof, derivatives thereof, and combinations thereof. The hydrocarbon can include a mixture or combination of two or more carbonaceous materials or a mixture or combination of two or more low ash or no ash polymers, biomass-derived materials, or by-products derived from manufacturing operations. The feedstock can include one or more recycled plastics such as polypropylene, polyethylene, polystyrene, derivatives thereof, blends thereof, or any combination thereof. Accordingly, the process can be useful for accommodating mandates for proper disposal of previously manufactured materials.

(7) Oxygen, or another suitable gaseous stream containing substantial amounts of oxygen is charged through conduit 16 into gasifier 14, and steam, or, if preferred, liquid water is introduced through conduit 18 to the gasifier 14. It is preferred that the process will be run continuously and at a substantially constant rate.

(8) Any one of several commercially available gasification processes can be incorporated into the process. Gasifiers such as the Texaco, the modified Koppers-Totzek and the Shell-Koppers or Lurgi are preferred, with the precise choice depending on the particular feedstock and overall integrated system. Recovery of at least some of the chemical energy converted to sensible heat.

(9) The gasifiers contemplated for use in the process may be operated over a range of pressures and temperatures between about 15 to 1500 psi and from 750 to 1200 C. The coal gasification product, or syngas, is then, in the broadest embodiment, prepared for the removal of impurities, acid gas constituents, water vapor and the like, as well as concentrating the hydrogen over CO to create a more desired. CO/H.sub.2 ratio for feed to a FT unit.

(10) Typically, the syngas product is purified by further processing in scrubbers or other apparatus to remove entrained solids and other contaminants, and then a variety of sulfur containing and other common acid gases (H, S, COS, CO.sub.2) are removed, preferably by conventional methods. The purification unit 28 can utilize pressure swing adsorption, nitrogen wash unit, cryogenic distillation, semi-permeable membranes, combinations thereof, and/or other purification processes. Absorbents used in the purification unit where applicable, can include caustic soda, potassium carbonate or other inorganic bases, and/or alanolamines. Upon exiting gas purifier, the cleaned, syngas is passed through conduit 20 to a CO.sub.2 separation/recovery unit 31 and then through the necessary alkyl formate product separation apparatus. After exiting the CO.sub.2 enrichment-unit through line 24, the conditioned syngas is fed to a FT unit 26.

(11) The carbon dioxide portion can be introduced to a CO.sub.2 compressor 32. The CO.sub.2 compressor can be any compressor suitable, or can include any configuration of multiple compressors of any suitable type. Suitable compressors can include, but are not limited to, centrifugal compressors, axial flow compressors, reciprocating compressors, combinations thereof, trains thereof, and/or the like. The CO.sub.2 compressor can produce a compressed carbon dioxide which can be sent to a heat recovery unit such as a molten salt reactor.

(12) In at least one preferred embodiment, pure oxygen, nearly-pure oxygen, essentially-pure oxygen, or oxygen-enriched air from an oxygen plant or air separation unit (ASU) can provide a nitrogen-lean and oxygen-rich gas (hereafter oxidant) via line. The oxidant via line can be coupled to the gasifier 14, thereby providing at least a portion of the oxidant thereto. The use of pure or nearly-pure oxygen gas as the oxidant can allow the gasifier 14 to produce raw syngas that can be essentially nitrogen-free, e.g., containing less than about 0.5% nitrogen and/or argon. Accordingly, in at least one specific embodiment, a single ASU can provide the oxidant for the gasifier 14. In one or more embodiments, the ASU can provide from about 10%, about 30%, about 50% about 70%, about 90%, or about 100% of the total oxidant fed to the gasifier 14.

(13) A novel feature of the present process involves a cooling step involving heat recovery using heat exchanger technology to gain carbon neutral energy used to drive the conversion/dissociation of CO.sub.2 into oxygen and carbon (in the molten metal reactor). The formation of oxygen from CO.sub.2 conversion will be used for the gasification of the coal. This creates a loop for the oxygen going into the gasifier, then being used in the coal conversion, producing CO and CO2; the CO2 will be dissociated to form oxygen (and carbon) and the oxygen will be fed back into the gasifier. The recovered heat energy form the syngas will be directed to heat the molten salt reactor that will be used to dissociate CO2 into O and C. The molten salt reactor has been demonstrated previously to electrochemically convert CO.sub.2 to activated carbon and oxygen. The activated carbon is an additional value added product. The oxygen will be directed to the oxygen plant that is a required part of the coal gasification process. Heat recovery is achieved using heat exchangers, or other alternate energy generation processes such as a electricity to heat the molten salt reactor to a selected temperature, for example about 500 C. The molten salt reactor has two electrodes. At the anode, high surface area carbon will be deposited and oxygen will be released at the cathode. The molten metal salt reactor is one example to use the carbon-neutral heat energy to dissociate CO.sub.2 into carbon and oxygen. The molten metal salt reactor can be further improved by modification of the electrodes and catalysts used in the electrodes to improve the catalytic performance and electrochemical conversion efficiencies.

(14) In the present invention, the CO.sub.2 from the syngas reaction is recovered and concentrated to serve as the feed to the molten salt reactor (MSR) which is heated at least partially by recirculating the syngas product there through which cools the syngas product for further processing and recovers the heat for the conversion of the CO.sub.2 to form a pure carbon by product for use as a catalyst or other carbon by products and produces pure oxygen which can be used to supplement the oxygen feed to the gasifier.

(15) The syngas product can be coupled to a Fischer Tropsch reactor or any other chemical conversion setup that utilizes a CO/H2 mixture. For example, the syngas product can be used to produce one or more FT) products, including refinery/petrochemical feedstocks, transportation fuels, synthetic crude oil, liquid fuels, lubricants, alpha olefins, waxes, and combinations thereof. The reaction can be carried out in any type reactor, e.g., fixed bed, moving bed, fluidized bed, slurry, bubbling bed, etc using copper, ruthenium, iron or cobalt based catalysts, or combination thereof, under conditions ranging from about 190 C. to about 450 C., depending on the reactor configuration. Additional reaction and catalyst details can be found in U.S. patent application Ser. No. 11/109,122 and U.S. Pat. Nos. 5,621,155; 6,682,711; 6,331,575; 6,313,062; 6,284,807; 6,136,868; 4,568,663; 4,663,305; 5,348,982; 6,319,960; 6,124,367; 6,087,405; 5,945,459; 4,992,406; 6,117,814; 5,545,674 and 6,300,268, the entirety of each being herein incorporated by reference, to the extent not inconsistent with this disclosure.

(16) The F-T products are liquids, which can be shipped to a refinery site for further chemically reacting and upgrading to a variety of hydrocarbon products including paraffin solvents which can be hydro treated to remove olefin impurities, or employed without hydrotreating to produce a wide variety of wax products. Liquid hydrocarbon products of C16+ can be upgraded by various hydroconversion reactions such as by hydrocracking, hydroisomerization catalytic dewaxing, isodewaxing, or combinations thereof, to produce mid-distillates, diesel and jet fuels such as low freeze point jet fuel, high cetane jet fuel, and the like. In addition isoparaffinic solvents, lubricants, lube oil blending components and lube oil base stocks suitable for transportation vehicles, non-toxic drilling oils suitable for use in drilling muds, technical and medicinal grade white oil, chemical raw materials, and various specialty products are useful derivatives.

(17) Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values are about or approximately the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

(18) Various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.

(19) While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.