As should by now be thoroughly familiar to our readers, there exist a multitude of variations on the basic technology for the indirect conversion of Coal into liquid hydrocarbons.
In such processes, most often labeled generically as "Fischer-Tropsch" syntheses, Coal and/or other Carbon source material is partially oxidized, i.e., partially combusted, in the presence of various, often proprietary, mixes of gases, such as Oxygen, Steam, and, perhaps surprisingly, Carbon Dioxide, thus forming, as product, a synthesis gas, or "syngas", blend of Carbon Monoxide and Hydrogen.
That synthesis gas can then be passed over one of, or a combination of, a surprisingly broad selection of well-known, and currently utilized, catalysts, where the Carbon Monoxide and Hydrogen are reacted to form an again surprisingly broad selection of hydrocarbons and/or oxygenated hydrocarbons, i.e., various alcohols.
The technology, as we've many times documented, originated in Europe in the 1920's, and was widely used throughout Europe and Asia by the Axis powers during WWII to produce liquid hydrocarbon fuels from Coal.
Development of the technology continued in the United States after WWII, with some major advancements made, wherein any co-production of Carbon Dioxide that might occur during the Coal gasification could be minimized, as seen for one example in our report of:
West Virginia Coal Association | Texaco 1957 CO2-Free Syngas from Coal | Research & Development; concerning: "United States Patent 2,803,530 - Production of Carbon Monoxide from a Solid Fuel; 1957; Assignee: Texaco Development Corporation; Abstract: This invention relates to a process for the generation of carbon monoxide and hydrogen from a solid carbonaceous fuel. In one of its more specific aspects, this invention relates to an improved method for the reaction of powdered coal with oxygen and steam to produce carbon monoxide and hydrogen.Coal ... may be reacted with a restricted quantity of free oxygen at temperatures above about 1,800F to produce carbon monoxide and hydrogen relatively free from carbon dioxide. Carbon monoxide, hydrogen and mixtures thereof are useful in a number of industrial processes. For example, liquid hydrocarbons suitable for use as motor fuels may be produced by reaction of hydrogen with carbon monoxide in the Fischer-Tropsch type synthesis reaction".
And, the petroleum industry continued to refine their Coal syngas generation and subsequent hydrocarbon synthesis technology over ensuing decades, developing different techniques to maximize the production of desired hydrocarbons; and, to minimize the co-production of Carbon Dioxide, and/or to productively utilize, and to a certain extent consume, any CO2 that might be co-produced, as seen, for two examples, in:
West Virginia Coal Association | Mobil Converts Coal to High Octane Gasoline | Research & Development; concerning: "United States Patent 3,972,958 - Conversion of Coal to High-Octane Gasoline; 1976; Assignee: Mobil Oil Corporation; Abstract: An integrated process for converting coal to high octane gasoline by gasifying the coal in such manner as to form a gas comprising carbon oxides, hydrogen and methane; contacting this gas in one or a series of steps with one or a series of catalysts (as specified) to produce alkylate gasoline"; and:
West Virginia Coal Association | Mobil Oil 1986 Coal to CO2-free Hydrocarbon Syngas | Research & Development; concerning: "United States Patent 4,583,993 - Carbon Monoxide and Hydrogen from Carbonaceous Material; 1986; Assignee: Mobil Oil Corporation; Abstract: Hydrogen and carbon monoxide are produced from coal, char or other carbonaceous material in a processing combination comprising a catalytic CO generator employing as reactant materials, fluid carbon material and CO2 product of the reaction of steam with CO to produce hydrogen and CO2. CO2 produced in the process is relied upon as the primary endothermic heat source in the fluid CO generator. The present invention is concerned with producing a clean gas composition of hydrogen and carbon monoxide from coal which is free of sulfur and nitrogen. A further object of this invention is to produce ... hydrogen and carbon monoxide which can be blended to form any desired ratio thereof for syngas conversion with a Fischer-Tropsch synthesis".
And, such technologies became even further refined, to the point where Carbon Dioxide from sources external to the Coal gasification process could be both directly, and, through the inclusion of renewable, Carbon Dioxide-recycling organic materials with Coal in the gasification process, indirectly consumed, as seen for example in:
West Virginia Coal Association | Conoco 2011 Coal + CO2 + H2O + O2 = Syngas | Research & Development; concerning: "United States Patent 7,959,829 - Gasification System and Process; 2011; Assignee: ConocoPhillips Company; Abstract: A system and process for gasifying carbonaceous feedstock with staged slurry addition in order to prevent the formation of tar that causes deposition problems.Claims: A process for gasification of a carbonaceous material, comprising the steps of: a. introducing a dry feedstock comprising ... particulate carbonaceous material into a reactor ... and partially combusting therein with a gas stream comprising an oxygen supply selected from a group consisting of oxygen-containing gas, steam, and mixtures thereof, thereby evolving heat and forming products comprising synthesis gas and molten slag; (and) ... wherein said carrier liquid is selected from group consisting of water, liquid Carbon Dioxide, (or) mixtures thereof (and) wherein said particulate carbonaceous material ... includes lignite, bituminous coal, sub-bituminous coal, or any combination thereof. Additional carbonaceous materials are coke from coal, coal char, coal liquefaction residues, particulate carbon, ... biomass, concentrated sewer sludge, bits of garbage, rubber and mixtures thereof".
In any case, however, some Carbon Dioxide does manage, via one route or another, to "leak" through into the product synthesis gas; which is, as we will explain a bit further on, not in and of itself that bad a thing. The Carbon Dioxide can be made, again as we will see further on, to itself react with Hydrogen in the synthesis reactor, with the subsequent formation of "oxygenated hydrocarbons", i.e., alcohols.
To avoid the effort and cost of having to separate straight hydrocarbons and oxygenated hydrocarbons from each other in the product mix emerging from the synthesis reactor, however, it might be more efficient to remove, and reclaim, any residual CO2 from the hydrocarbon synthesis gas itself, after it has, as in the above-referenced "United States Patent 7,959,829 - Gasification System and Process", been generated from "coal ... biomass, concentrated sewer sludge, bits of garbage, rubber and mixtures thereof".
And, that is the purpose of a whole suite of technologies developed by the Continental Oil Company, now Conoco, and it's constituent business units, which, at least at one time, included Consolidation Coal Company, Consol.
As explained, via our initial introduction of the technology, in excerpts from the initial link in this dispatch to:
"United States Patent 4,191,538 - Synthetic CO2 Acceptor and Gasification Process Therewith
Date: March, 1980
Inventor: Everett Gorin, CA
(Please recall Consol's prolific and award-winning Coal conversion genius, Everett Gorin; who, as seen for one example in our report of:
Consol 1953 Coal to Hydrogen & Methane with No CO2 | Research & Development; concerning: "United States Patent 2,654,661 - Gasification of Carbonaceous Solid Fuels; 1953; Inventor: Everett Gorin, PA; Assignee: Consolidation Coal Company, Pittsburgh; Abstract: This invention relates to the gasification of carbonaceous solid fuels, and particularly to the production of hydrogen or high B.t.u. gas from such fuels";
toiled, before his semi-retirement to the sunnier west coast, for many decades in one of the cloudy hearts of US Coal Country on the conversion of our abundant Coal into various hydrocarbon products. - JtM)
Assignee: Continental Oil Company, CT
This invention resulted from work done pursuant to a contract with the Energy Research and Development Administration (now Department of Energy).
Abstract: A synthetic CO2 acceptor comprising at least one compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix of the general formula 3CaO(SiO2)x (Al2O3)x wherein x is from about 0 to about 1.0.
(All stuff we can get from sand, limestone and aluminum ore. It would be inexpensive. - JtM)
Claims: A synthetic CO2 acceptor consisting essentially of at least one chemically uncombined calcium compound selected from the group consisting of calcium oxide and calcium carbonate supported in a refractory carrier matrix ... .
In a process for producing a synthesis gas by reacting a carbonaceous feedstock with water in the presence of a carbon dioxide acceptor to produce a synthesis gas rich in hydrogen with at least a portion of the carbon dioxide so produced being reacted with said calcium oxide to produce calcium carbonate, the improvement wherein, said CO2 acceptor consists essentially of at least one chemically uncombined calcium compound selected from the group consisting essentially of calcium oxide and calcium carbonate supported in a refractory carrier matrix ... .
The improvement ... wherein said acceptor is contacted with steam at a pressure (and) a temperature (as specified) after at least a portion of said calcium oxide has reacted to produce calcium carbonate.
The improvement ... wherein said steam contacting is at a pressure from about 10 atmospheres to about 20 atmospheres and a temperature from about 1200 F to about 1600 F.
The improvement ... wherein a CO2 pressure up to about one atmosphere is present during said steam contacting.
The improvement ... wherein said acceptor is regenerated by heating said acceptor to a temperature in excess of 1800 F thereby converting said calcium carbonate to calcium oxide.
Description: This invention relates to synthetic CO2 acceptors for use in processes wherein steam and carbonaceous fuels are reacted in the presence of calcium oxide to produce gaseous products and calcium carbonate.
In view of the continuing and well-known shortage of natural gas and similar fuels, a continuing effort has been directed to the development of methods whereby synthetic natural gas and other substitutes for naturally-occurring gaseous fuels can be produced from coal and other solid carbonaceous fuels. One such method has been the direct reaction of steam with carbonaceous fuels such as coal, coke and the like in the presence of calcium oxide to produce gaseous products which are rich in hydrogen and calcium carbonate.
In accordance with the present invention, a synthetic acceptor is provided. The synthetic acceptor of the present invention comprises, in essence, a thermally stable inert matrix which is a porous refractory carrier which is substantially inert to lime and the high temperature steam environments encountered in the (Coal gasification) process ... .
The use of the synthetic acceptor of the present invention permits the use of higher steam pressures, i.e. in excess of 13 atmospheres ..., since the synthetic acceptor of the present invention is readily regenerated by the formation of a relatively low melting eutectic mixture of calcium oxide, calcium hydroxide and calcium carbonate which forms in the presence of steam. The calcium compounds, i.e. calcium oxide, calcium carbonate or mixtures thereof, of the synthetic acceptor are held within the refractory matrix by surface tension or the like so that the calcium compounds are at least partially liquefied as the synthetic acceptor passes through the process, thereby regenerating the synthetic acceptor with each passage through the process.
The reaction of the calcium carbonate and carbon dioxide liberates substantial quantities of heat which is required to sustain the reaction of carbon with steam. Since substantial quantities of carbon dioxide are removed from the reaction zone, the synthesis gas mixture so produced is rich in methane and, particularly, is rich in hydrogen since the removal of the CO2 tends to result in a substantial shifting of the equilibrium composition to hydrogen."
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We'll close our excerpts there, so that we can summarize, and, emphasize a few important things that, unfortunately, aren't clearly stated in any of the Carbon Dioxide Acceptor technologies we've studied so far.
However, first, please note that, as above, the "reaction of the calcium carbonate and carbon dioxide liberates substantial quantities of heat which is required to sustain the reaction of carbon with steam", using Carbon Dioxide Acceptors in a Coal gasification can generate some of the heat needed for that gasification, thus limiting the amount of Carbon that must be fully oxidized to generate heat for, and, consequently, also reducing the amount of Carbon Dioxide generated during, the gasification.
Further, as Gorin and other Consol scientists explained more than forty years ago:
http://web.anl.gov/PCS/
"Carbon Dioxide Acceptor Gasification Process; G. P. Curran, C. H. Rice and E. Gorin; Consolidation Coal Company; Production of both hydrogen rich and high BTU gas from coai has been under study in the Research Division of Consolidation Coal Company for several years. There are a number of partially or fully developed processes which are available for this purpose. It is a feature of most of the available processes that oxygen is used to provide the endothermic heat of the gasification process. The high cost of oxygen is one of the more significant items which makes the conventional processes uneconomic. It has thus become clear that elimination of oxygen is one of the prerequisites for the development of an improved process. The CO2 acceptor process is one which satisfies this general objective. This paper describes some steps which have been taken in the development of the process. The emphasis is on a discussion of the properties of the acceptor as determined by the needs. The general principle of the CO2 acceptor process is the use of a circulating lime-bearing acceptor. The acceptor generates the heat required in the gasification step of the process by the reaction, CaO + CO2 = CaCO3. The absorption of carbon dioxide serves also to enrich the gas in hydrogen. More heat is thus evolved by intensification of the two exothermic reactions: CO + H2O = CO2 + H2 (and) C + 2H2 = CH4 (and, it) thus becomes possible to supply all the heat requirements of the gasification process by use of a suitable acceptor";
such use of a CO2 Acceptor can not only provide all of the heat energy required to effect the Coal gasification, it can also help to promote the co-generation of some Methane, CH4.
We are going to be addressing the advantages of Carbon Dioxide Acceptor technologies more fully in future dispatches; but, one thing that is rarely made clear is, that, in the regeneration of the Acceptor, for recycling to the gasification process, which is most often accomplished by treating the CO2-loaded Acceptor with Steam at high temperatures, Carbon Dioxide gas is liberated into the treating Steam.
That fact and process is more clearly explained in a closely-related and derivative technology, disclosed in:
"United States Patent: 5520894 - Removing Carbon Dioxide Regeneratively from Gas Streams
Date: May, 1996
Inventor: Albertus Heesink, et. al., Netherlands
Abstract: A process for removing carbon dioxide regeneratively from a hot gas stream, containing flue gases or fuel gases, wherein the gas stream is successively: a) used for heating and/or desorbing a solid absorbent loaded with carbon dioxide ... (as) discharged (from the gasifier); and wherein: the absorbent ... is desorbed ... at least partially and optionally under elevated pressure ... ((desorbing at least partially the CO2 from the absorbent (in a step) where the heat from the hot gas stream liberates at least a portion of the CO2 from the CO2-loaded absorbent thereby regenerating the absorbent)).The process and the system are suitable for removing carbon dioxide from combustion gases and for shifting (coal) gasification gases toward hydrogen".
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We'll attempt to do a better job in our future reports concerning Carbon Dioxide Acceptors of explicitly documenting the Acceptor regeneration process.
That is, we think, important, since all of them seem to specify treatment of the loaded Acceptor with Steam at high temperatures to effect the regeneration; a process which leads to liberation of the Carbon Dioxide, which is then carried off in the Steam.
And, we remind you of one previous report, among a number related, as accessible via:
More USDOE CO2 "Syntrolysis" | Research & Development; concerning: "Co-Electrolysis of Steam and Carbon Dioxide for Production of Syngas; 2007; USDOE; and Ceramatec, Inc.; Abstract: An experimental study has been completed to assess the performance of single-oxide electrolysis cells ... simultaneously electrolyzing steam and carbon dioxide for the direct production of syngas ... a mixture of hydrogen and carbon monoxide (which) can be used for the production of synthetic liquid fuels via Fischer-Tropsch processes";
wherein it's explained just how useful such a blend of Steam and Carbon Dioxide, as co-produced via a technology such as that explained by our subject herein, "United States Patent 4,191,538 - Synthetic CO2 Acceptor and Gasification Process Therewith"; wherein the Steam and the Carbon Dioxide are byproducts of a process for, as specified, making "synthetic natural gas and other substitutes for naturally-occurring gaseous fuels ... from coal", could be.