Gasification of carbonaceous solids
We recently sent you report of a process developed by ExxonMobil, a seemingly-advanced technology which enables the co-conversion of both Coal and Carbon-recycling organic materials into a synthesis gas blend of Carbon Monoxide and Hydrogen, a gas mixture which would be suitable for catalytic chemical condensation into liquid hydrocarbon fuels.
That report is now accessible via:
Exxon Co-Gasifies Coal and Carbon-Recycling Biomass | Research & Development; and details:"United States Patent Application 20100083575 - Co-gasification Process for Hydrocarbon Solids and Biomass; 2010; ExxonMobil Research and Engineering Company, NJ; Abstract: A process for the co-gasification of carbonaceous solids (coal) and biomass ... wherein the solid carbonaceous particles comprise coal (and) wherein the biomass comprises biological matter selected from wood, plant matter, municipal waste, green waste, byproducts of farming or food processing waste, sewage sludge, black liquor from wood pulp, and algae (which would enable) the production of hydrocarbon liquids (via) the gasification ... followed by the conversion of the produced synthesis gas to form liquids by processes such as Fischer-Tropsch".
And, it just goes to show you that the more things change, the more they stay the same.
The information we submit in this dispatch would seem to indicate that ExxonMobil's New Jersey scientists were actually just rooting around in the file archives down in the basement one day, maybe for something to do during lunch break, and stumbled across a forgotten artifact, an antique they decided to haul upstairs and dust off, so that everyone could have another look at it.
But, we don't want our modest attempt at narrative composition to detract from the significance of what we bring to your attention herein, which is:
Fully one half of a century ago, scientists in the employ of one of the companies that ultimately coalesced into ExxonMobil developed a technology wherein both Coal and sustainable, Carbon-recycling organic products of botanical origin could be converted together, in the same processor, into a blend of Hydrogen and Carbon Monoxide synthesis gas suitable, as is that generated by the above-noted process of United States Patent Application 20100083575, for catalytic condensation into hydrocarbons.
Comment follows excerpts from the initial link in this dispatch to:
"United States Patent 2,554,263 - Gasification of Carbonaceous Solids
Date: May, 1951
Inventor: Karl Nelson, NJ
Assignee: Standard Oil Development Company, a corporation of Delaware
Abstract: The present invention relates to the conversion of carbonaceous solids such as all types of coal, lignite, peat, ... cellulosic materials, etc., into gases containing carbon monoxide such as water gas, producer gas and the like.
Prior to the present invention, it has been suggested to gasify carbonaceous solids with a gasifying medium such as steam and/or air to produce water or producer gas (from a) dense turbulent bed of finely divided solids ... fluidized by an upwardly flowing gas ... .
This technique is greatly superior to conventional fixed bed operation (in that it) provides larger solid reaction surfaces, better mixing and greatly improved temperature control, and it affords higher gas yields in fully continuous operation within shorter reaction times.
(Obviously, they knew a lot about hydro-gasifying Coal fully one half of a century ago.)
While these great advantages make the application of the fluid solids technique to coal gasification appear highly attractive it has not as yet found the broad commercial application it would seem to deserve.
(The more things change, the more they stay the same. True then. True now.)
One of the more important reasons of the slowness of this development lies in difficulties encountered in the substantially complete conversion of the carbon feed with the carbonaceous charge into product gas and heat required for the process at reasonably constant conversion conditions, satisfactory steam conversion rates, reasonable temperature levels and economic equipment design.
Such substantially complete utilization of the carbonaceous charge is an essential condition for the economic operation of the coal gasification process.
It is, therefore, an important object of this invention to provide an improved process for producing combustible gases from carbonaceous solids employing the fluid solids technique.
Another object ... is to provide an improved process for the gasification of carbonaceous solids at optimum rates of conversion and with full utilization of available carbon.
(The full Disclosure, like many dating from this era and earlier, resorts to over-description and archaic wording that is tedious in the extreme. In brief sum, still-carbonaceous residues from an initial gasification zone are transferred to a second reactor, where they are combusted with Oxygen. The heat generated from that combustion is collected and transferred to the initial Coal gasification zone, as are the flue gases resulting from that combustion of the Coal gasification residues. The added heat helps to drive some of the endothermic reactions in that initial Coal gasification reactor, as they go on to explain, which reactions include most of the Carbon Dioxide in that flue gas being converted into Carbon Monoxide through reactions with the hot Coal.)
Complete combustion of the carbon supplied as gasification residue to the combustion zone normally requires a considerable excess of oxygen to be supplied to the combustion zone. This excess oxygen enters the gas generator as a constituent of the high temperature flue gas so that the heat balance required for the conversion of carbon and gasifying medium into fuel gas is established by the fast and extremely exothermic reaction between oxygen and carbon, for example, in accordance with the following equations:
1. C + O2 = CO2 + 170,000 B.t.u.
2. C + CO2 = 2CO - 74,500 B.t.u.
3. CO + H2O = CO2 + H2 + 18,000 B.t.u.
(We must, as one of our adept consultants urges, interrupt here, at some unfortunately great length, to point out a few things. The combined reactions "1" and "3", above, yield a total of 188,000 British thermal units of heat energy. Yet, reaction "2", wherein Coal is reacted with Carbon Dioxide to yield Carbon Monoxide, requires only 74,500 Btu's to drive it. That leaves a large excess of heat energy, which could be used to drive another reaction, i.e.,:
C(oal) + H2O = CO + H2.
However, we're advised, the balance of components would still be off, so that there would an excess of Carbon Monoxide, beyond that which could be reacted with the Hydrogen, made available.
And, in fact, though it won't be reflected in our excerpts, the full Disclosure of our subject, USP 2,554,263, does go on to explain that a small portion of the CO2 that is generated must be extracted from the product gases and simply vented, to prevent the formation of excess Carbon Monoxide. Such excess CO could, as in Equation "3", be reacted with more Steam, to make more Hydrogen, but, that would generate more CO2 which would have to be recycled into the reaction of Equation "2". Alternatively, it was suggested to us that, rather than use the process of Equation "3" to generate Hydrogen, along with more Carbon Dioxide, the excess energy of Equation "1" be directed, perhaps by being first converted into electricity, into a process such as that seen in:
USDOE Makes Hydrogen by Using Sulfur Dioxide | Research & Development; concerning: "United States Patent 4,244,794 - Hydrogen Production by the Decomposition of Water; 1981; Assignee: The United States of America; Abstract: Water and SO2 react in (an) electrolyzer ... so that hydrogen is produced at the cathode and sulfuric acid is produced at the anode";
wherein a pollutant, SO2, which might in the first place be scrubbed from the Coal synthesis gas, is reacted with H2O, and made to produce both the small amount of additional Hydrogen seemingly needed by the process of our subject, US Patent 2,554,263, to consume any excess Carbon Monoxide made from CO2, and, as a by-product, commercially valuable Sulfuric Acid.
Or, perhaps of even more interest, the extra Hydrogen could be acquired from a process like that seen in:
USDOE Algae Make Hydrogen for Coal and CO2 Hydrogenation | Research & Development; concerning: "Photosynthetic Hydrogen and Oxygen Production by Green Algae; Oak Ridge National Laboratory; Tennessee; 1999; USDOE;
wherein it's confirmed that certain strains of Green Algae can be harnessed to recycle industrial effluent Carbon Dioxide, and do several things in the course of their metabolic processing of CO2:
First, they produce "bio-lipids", which can be harvested and converted rather easily into Diesel fuel. Second, in the cyclic course of their metabolism, through periods of dark and light, some Algae, as in the USDOE report above, will generate and produce recoverable Hydrogen gas, which could then be used to satisfy the apparent Hydrogen deficit of Standard Oil's process of United States Patent 2,554,263. As a bonus, once the excess Algae were harvested, and subjected to extraction of their lipids content for Diesel fuel production, their remaining cellular debris, consisting mostly of cellulose, could be recycled into the feed of our subject US Patent 2,554,263, which, as specified by Standard Oil, would consist of "coal (and) cellulosic materials".
If all of that is too much trouble, however, we could instead take any excess Carbon Monoxide, and, as the Petroleum industry knew how to do when our subject US Patent 2,554,263 was issued, simply, as seen in:
Pittsburgh 1951 Carbon Monoxide + Water = Hydrocarbons | Research & Development; concerning: "United States Patent 2,579,663 - Process of Synthesizing Hydrocarbons; 1951; Assignee: Gulf Research and Development Company, Pittsburgh; Abstract: This invention relates to a process for synthesizing hydrocarbons; more particularly the invention relates to a process for synthesizing normally liquid hydrocarbons from carbon monoxide and steam";
react the excess Carbon Monoxide with plain old H2O and make some "liquid hydrocarbons".)
An additional advantage of my invention results from the fact that gas-generating equipment for high-carbon, low-temperature operation is more economical with respect to size and cost of construction materials than equipment for low-carbon and/or high-temperature operation.
As (noted), the external combustion zone is normally operated with an excess of oxygen so that unconverted oxygen becomes available for conversion and/or heat generation within the (primary) gas generation zone. For the generation of producer gas this excess of oxygen may be chosen high enough to supply, in combination with the CO2 content of the flue gas, all the oxygen required in the (primary) gas generation zone to convert the desired amount of carbon into carbon monoxide."
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We are compelled to terminate our excerpts there, since the rest of the Disclosure does go on to describe in great detail how converting "the desired amount of carbon into carbon monoxide" is to be achieved, with special attention being paid to the management of the Carbon Dioxide, so that, as we indicated above, production of an excess of Carbon Monoxide is avoided.
Our thoughts, again, are that any excess of Carbon Monoxide, relative to Hydrogen, when the final product gas mixture is intended for catalytic condensation, as via the Fischer-Tropsch, or similar, technologies, into liquid hydrocarbons, can be offset by Hydrogen supplied from outside the process, such as, for an even additional example, in our report of:
NASA Hydrogen from Water and Sunlight | Research & Development; which concerns: "United States Patent 4,045,315 - Solar Photolysis of Water; 1977; NASA; Abstract: Hydrogen is produced by the solar photolysis of water";
which would, as would the "Photosynthetic Hydrogen and Oxygen Production by Green Algae", as cited above, also generate some of the concentrated Oxygen needed by the process of US Patent 2,554,263.
But, we do note that the amounts of CO2 which are specified by Standard Oil to be vented from the process represent, in any case, only a very, very small percentage of the total raw material Carbon fed to it.
And, even if the excess CO2 were left unutilized, it would represent, accordingly, depending upon the amounts of the specified "cellulosic materials" that were fed, along with Coal, into the initial gasification stage, only a minor percentage of the total Carbon Dioxide that was thus, as a result of the photosynthetic processes that went into the formation of those "cellulosic materials", actually being utilized and recycled, in a process for making a synthesis gas, like that generated in a fashion very similar to that disclosed by ExxonMobil in their much more recent:"United States Patent Application 20100083575 - Co-gasification Process for Hydrocarbon Solids and Biomass", as cited above, which enables "production of hydrocarbon liquids (from such a) synthesis gas ... by processes such as Fischer-Tropsch".