Gasification of carbonaceous solid fuels
We've lately been documenting the fact that Coal can be gasified, i.e., converted into a synthesis gas mixture of Hydrogen and Carbon Monoxide well-suited for catalytic chemical condensation into liquid hydrocarbons, with very little co-production of Carbon Dioxide, by supporting the necessary partial oxidation reactions with an Oxygen donor substance, rather than with Air or purified Oxygen.
A recent example of that reportage would include:
Oklahoma Oxygen Donor Coal Gasification | Research & Development; which concerns: "United States Patent 4,073,630 - Production of Carbon Monoxide; 1978; Phillips Petroleum Company; Abstract: In a system wherein carbon monoxide is produced from a carbon source by contacting the carbon source with solid zinc oxide in a primary reaction zone, zinc values which are entrained in the ash byproduct are recovered, reconverted to zinc oxide and reused for production of additional carbon monoxide in a secondary reaction zone wherefrom the zinc is recovered, reconverted to zinc oxide and thereafter reused in the primary reaction zone".
The rational behind development of such technology is based on the several advantages it offers.
First, it avoids the co-production, through the use of plain air as the oxidant, of unwanted Nitrogen Oxide pollutants, which wastes both heat energy and Oxygen, and which might someday require expensive exhaust gas treatment.
Second, the use of Oxygen donors to achieve the above-noted advantages is less expensive than the processes of separating and concentrating purified Oxygen from the air to the same end.
Third, the selection of a proper Oxygen donor can enable the co-production of the Hydrogen needed for combination with the relatively pure Carbon Monoxide generated from Coal through use of that Oxygen Donor, as in the Phillips Petroleum "United States Patent 4,073,630 - Production of Carbon Monoxide"; cited above, wherein the Zinc Oxide is regenerated, after donating Oxygen to Coal, through reaction with water or steam, which reaction synergistically generates Hydrogen as a by-product.
Somewhat unsurprisingly, those potentials were recognized and studied a long time before Phillips Petroleum, as above, stumbled onto them, by Consolidation Coal Company's award-winning Coal conversion scientist, Everett Gorin.
We've previously cited Gorin many times of course, but we call your attention to one report in particular, as now accessible via:
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; Assignee: Consolidation Coal Company; 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. In application Serial No, 99,561, filed June 16, 1949, a process for the gasification of carbonaceous solid fuels by reaction between steam and solid fuels in the presence of calcium oxide is described."
We remain uncertain as to the fate of Gorin's US Patent Application 99,561, as he himself cites above; but, herein, we see that what seems a very similar-sounding technology developed by him, though using a slightly different Oxygen donor substance, was, in the same frame, found by our US Government's expert patent examiners to be a sound and practical innovation.
We must note that the title of our current dispatch might be seen as a little misleading.
The hydrocarbon synthesis gas produced by our subject process herein is itself indeed free of Carbon Dioxide; but, the process itself is not. Carbon Dioxide is generated, but in a way that both keeps it out of the synthesis gas blend of Carbon Monoxide and Hydrogen and later separates it in a concentrated form convenient for disposition through other processes.
It is not so much "CO2-Free" as it is "CO2-deferred".
As we attempt to explain, in comment inserted within, and appended to, our excerpts from the initial link in this dispatch to:
"United States Patent 2,682,457 - Gasification of Carbonaceous Solid Fuels
Date: June, 1954
Inventor: Everett Gorin, PA
Assignee: Consolidation Coal Company, Pittsburgh
Abstract: This invention relates to the gasification of carbonaceous solid fuels, and, more particularly, to methods of and apparatus for reacting carbonaceous solid fuels with steam.
(An) object of this invention is to provide a process in which steam reacts with solid carbonaceous fuels to yield a gaseous product under such conditions that no heat need be added to the system to maintain the reaction, i.e., under thermoneutral conditions.
(Note that "thermoneutral" means that no source of heat energy external to the gasification process needs to be supplied to that gasification process. All of the needed heat for all of the endothermic reactions, including the dissociation of H2O into Hydrogen and Oxygen, is generated by other, exothermic, reactions within the total system. A previous example of our reportage concerning similar potentials can be seen in:
1963 Self-Powered Coal Conversion | Research & Development; concerning: "US Patent 3,107,985 - Coal (and it's) Autogenous Hydrogenation; 1963;
Unlike the Huntington process of "United States Patent 3,107,985", however, our subject Consol process of "United States Patent 2,682,457" doesn't rely on a separate, and CO2-generating, partial combustion process to provide the thermal energy.
The term "thermoneutral" has also been described in terms of "heat balance" in other of our reports; and, there are some special sorts of chemical reactions occurring in Consol's disclosed process pertaining to that concept, which, given both the current absence of our former technical advisors and our limited capacities, we will do our best to explain as we go along.)
A further object of this invention is to provide an improved process for making a high B.t.u. fuel gas which is rich in methane from the reactions between steam and carbonaceous solid fuels.
(We must again interject to remind you, that, should we choose to synthesize Methane, as above, from Coal, in this "thermoneutral" and essentially Carbon Dioxide-free process, then we can utilize that Methane, as explained for just one example in:
Standard Oil 1987 CO2 + CH4 = Syngas | Research & Development; concerning: "United States Patent 4,690,777 - Production of Synthesis Gas; 1987; The Standard Oil Company; Abstract: Gas mixtures containing at least hydrogen and carbon monoxide are prepared by reforming ... light hydrocarbons (in a process) comprising contacting the light hydrocarbons with carbon dioxide ... (and) wherein the light hydrocarbon is methane. (Gas) mixtures containing carbon monoxide/hydrogen ratios of 1/1 or 1/2 are particularly useful as feed gases in processes for producing higher hydrocarbons and oxygenated derivatives, such as Fischer-Tropsch and alcohol synthesis processes";
to consume Carbon Dioxide collected from whatever source, perhaps a raw Shale Gas stripping facility, in reactions that convert them both into a blend of Carbon Monoxide and Hydrogen suitable for conversion into liquid hydrocarbon fuels through the "Fischer-Tropsch and alcohol synthesis processes". We ask that you keep that concept in mind as you study the remainder of our excerpts.)
Still another object of my invention is to provide a method for converting carbonaceous solid fuels into a gas which is rich in hydrogen and which is substantially free of carbon dioxide.
In accordance with my invention, I utilize the reaction between steam and carbon to convert solid carbonaceous fuels into a gaseous product in the presence of strontium oxide.
(A note about "strontium": Though not as well-known as Calcium, it belongs to the same group as does Calcium in the Periodic Table of Elements and will have similar characteristics. As can be learned via:
Strontium - Wikipedia, the free encyclopedia; it is currently mined on a commercial basis in some parts of the world, it does have some current industrial uses; and, it is fairly abundant. If we want more of it, we can get it without breaking either the bank or too much of a sweat.)
I have discovered that when strontium oxide is mixed with carbonaceous solid fuels in the proper proportions and under certain critical conditions of temperature and pressure, the steam-carbon reaction is thermoneutral, i.e., no heat need be added to the system to maintain the reaction.
In fact, the reaction may even be exothermic and capable of generating the steam necessary for the process.
(That, too, would be an energy-conserving and CO2-preventing aspect of the technology.)
Moreover, it was found that under these thermoneutral conditions, gases which contained surprisingly high percentages of either methane or hydrogen can be selectively produced by operating under conditions lying within the critical range required to produce a themoneutral reaction.
(We again interject to note that Gorin goes on to specify the temperature and pressure ranges within which the reactions are to be conducted; and, they are both quite high. But, they are definitely within the boundaries of modern industrial engineering, although the process equipment would be expensive. However, a benefit is that, as explained by Gorin, the temperature and pressure can be adjusted, relative to each other, so that more, or less, Hydrogen is produced relative to Methane. The system can be "tuned", in other words, to generate the product most desired, though both, to one extent or another, will be made.)
More specifically, my new process comprises the use of strontium oxide and finely divided carbonaceous solid fuels in the proportions of at least 220 parts by weight strontium oxide to each 100 parts by weight of carbon contained in the fuels.
(That is a lot of Strontium Oxide relative to Coal; but, the Strontium itself is not to any appreciable extent consumed in or used up by the reaction, or passed on into product. The element Strontium is, in a sense, serving as more of an Oxygen transfer and Carbon capture agent than as an Oxygen donor. It facilitates, and reduces the energy required, to "take" Oxygen from Water, H2O, and then to "give" it, to Coal, or Carbon, while releasing Hydrogen from the H2O. It might also be seen as supporting a partial oxidation of Coal, thereby raising it to a temperature where the Carbon itself is hot enough to dissociate the Water molecules, combining with Oxygen and releasing Hydrogen.
The net result is Carbon Monoxide, CO, and Hydrogen, H2; and, ultimately, after some further processing of intermediate carbonate compounds, more Strontium Oxide looking around for more H2O to swipe Oxygen from and give to Carbon.
Again, Strontium isn't nearly as common or as cheap as the Calcium utilized in our above-cited Consol process of "United States Patent 2,654,661 - Gasification of Carbonaceous Solid Fuels". However, it does belong to the same group of metals as does Calcium, isn't used up by the reaction; and, we can get plenty more of it, need be.)
In accordance with my invention, the reaction between steam and carbonaceous solid fuels is carried out in a single vessel system utilizing an on-and-off cycle. Steam is first passed through a bed of strontium oxide and the carbonaceous solids to produce a gas containing hydrogen, methane, carbon monoxide and carbon dioxide by the reaction between steam and carbonaceous solids. Simultaneously strontium carbonate is formed in the vessel from the reaction between strontium oxide and the carbon dioxide in the gas produced, there being sufficient oxide present to convert carbon dioxide substantially completely to carbonate. The reaction between the strontium oxide and the carbon dioxide generates in situ the heat required to maintain the steam-carbon reaction ... .
During the off cycle, air or any gas containing oxygen is circulated through the vessel to regenerate the strontium oxide from the carbonate. Sufficient carbonaceous solids are oxidized during the regeneration to raise the temperature of the strontium carbonate above its dissociation temperature so that the carbonate breaks down into strontium oxide and carbon dioxide.
(And, there you have the Strontium Oxide regeneration process we mentioned in our opening comments, wherein the Carbon Dioxide trapped by Strontium Oxide, in the formation of Strontium Carbonate during the gasification process, is released in a nearly pure form. It is then free to be directed into another process, such as, for instance, that of the above-cited "United States Patent 4,690,777 - Production of Synthesis Gas", to be reacted with some of the Methane produced by our subject process herein of "United States Patent 2,682,457 - Gasification of Carbonaceous Solid Fuels", to make a synthesis gas suitable, as in the process of USP 4,690,777, for "Fischer-Tropsch and alcohol synthesis processes"; or, to be reacted with plain old H2O, via a technology similar to that described in:
Penn State Solar CO2 + H2O = Methane | Research & Development; concerning: "High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels; 2009; The Pennsylvania State University; Efficient solar conversion of carbon dioxide and water vapor to methane";
wherein freely-available environmental energy can be harnessed to convert the excess CO2 into more of the Methane primarily derived, via the process of our subject, Consol's "US Patent 2,682,457 - Gasification of Carbonaceous Solid Fuels", from Coal.