As further evidence of just how efficient and sophisticated the technology for converting our abundant Coal into more versatile liquid and gaseous hydrocarbons had, some several decades ago, among the closed circle of Big Oil, and US Government initiates, become, we recently submitted information concerning an improvement on Coal conversion technology, an improvement financed, through our US Government, by our tax dollars, that related to the recovery, and reuse, of metal catalysts from the residues of Coal conversion.
That information is now accessible on the West Virginia Coal Association's web site via the link:
Exxon Recovers and Recycles Coal Conversion Catalyst | Research & Development; and concerns:
"United States Patent 4,157,246 - Hydrothermal Alkali Metal Catalyst Recovery Process; 1979; Assignee: Exxon Research and Engineering Company; Abstract: In a coal gasification operation or similar conversion process carried out in the presence of an alkali metal-containing catalyst wherein solid particles containing alkali metal residues are produced, alkali metal constituents are recovered from the particles primarily in the form of water soluble alkali metal formates by treating the particles with a calcium or magnesium-containing compound in the presence of water ... and in the presence of added carbon monoxide. This process permits increased recovery of alkali metal constituents, thereby decreasing the overall cost of the gasification process by reducing the amount of makeup alkali metal compounds necessary (and) wherein said conversion process comprises gasification (or) wherein said conversion process comprises liquefaction (and) wherein said carbonaceous feed material comprises coal.The government of the United States of America has rights in this invention pursuant to Contract No. E(49-18)-2369 awarded by the U.S. Energy Research and Development Administration."
We, of course, wonder if the above is among the technologies that will be publicly exposited by ExxonMobil, this coming April, 2012 - - in the capitol city of China.
Such might well be the case, since, as seen in our report of:
China Celebrates Coal Liquefaction | Research & Development; wherein can learn that: "The World CTL 2012 Conference takes place on April 17-20, 2012 in China, featuring two World Best: The reference gathering of Coal Conversion experts and managers on April 17-19 in Beijing (and) the visit to the World’s Largest Coal-To-Olefins Plant on April 20 in Baotou (Inner Mongolia); and, that, the presentations to made include: Gasification: Syngas To products: Syngas To Methanol; Davy Process Technology, United Kingdom (and)Methanol To Gasoline; Mitch Hindman, ExxonMobil, USA";
they will certainly be there, and will be making presentation of at least some of their Coal conversion-related expertise.
And, herein, we present another facet of ExxonMobil's Coal conversion technology, which explains how, once they have the catalyst, perhaps as reclaimed and recycled from the above-cited process of "United States Patent 4,157,246", the catalyst is to be applied to the Coal, and both then gasified with Steam to form more hydrocarbon synthesis gas.
Comment follows, and is inserted within, excerpts from the initial link in this dispatch to:
"United States Patent 4,284,416 - Integrated Coal Drying and Steam Gasification Process
Date: August, 1981
Inventor: Nicholas Nahas, Baytown, TX
Assignee: Exxon Research & Engineering Company, NJ
Abstract: Carbonaceous solids slurried in an aqueous solution, which preferably contains catalyst constituents having gasification activity, are dried by contacting the slurry with superheated steam in a fluid bed slurry dryer and the resultant dried solids are subsequently gasified with steam generated in the dryer.
(We see in the above statement indication of a subtle, but perhaps important, efficiency: It's necessary that the catalyst be impregnated as deeply into the Coal particles as possible, which is accomplished by drying the "aqueous solution" containing the catalyst off of the particulate Coal "with superheated steam". But, nearly all Coal contains at least some quantity of somewhat volatile organic matter, lighter tars, for instance, which would be vaporized and driven off at the temperature of "superheated steam". Thus, by using the "steam generated in the dryer" that first dried the Coal and impregnated the Coal with the gasification catalyst, to then gasify the Coal, any volatile organic matter vaporized during the application of the catalyst would be directed into the gasification chamber; and less, or none, of the original Carbon content of the Coal would be lost. Further, such practice would reduce the potential for objectionable organic emissions from the catalyst application, pre-gasification procedure itself.)
Claims: A process for drying an aqueous slurry of carbonaceous solids containing water-soluble gasification catalyst constituents and subsequently gasifying the dried solids which comprises:
(a) contacting said aqueous slurry of carbonaceous solids containing said water-soluble gasification catalyst constituents with superheated steam in a fluidized bed drying zone, said superheated steam having a temperature sufficiently higher than the temperature in said drying zone to convert more than about 80 weight percent of the water in said slurry into steam and to deposit said water-soluble gasification catalyst constituents onto said carbonaceous solids;
(b) withdrawing carbonaceous solids of reduced water content and impregnated with said gasification catalyst constituents from said drying zone and passing said solids to a gasification zone maintained at gasification conditions;
(c) withdrawing steam from said drying zone and passing at least a portion of said steam to said gasification zone; and
(d) gasifying said catalyst impregnated carbonaceous solids in said gasification zone with said steam passed to said gasification zone.
2. A process ... wherein said carbonaceous solids comprise coal.
3. A process ... wherein a portion of said steam withdrawn from said drying zone is superheated and recycled to said drying zone to provide said superheated steam.
4. A process ... wherein the aqueous portion of said slurry comprises sour water produced by condensing unreacted steam from the gaseous effluent exiting said gasification zone.
(Thus, in the above Claim, any unreacted water vapor exiting the gasification process itself, which water vapor might be contaminated with organic products not broken down in the gasification, is also reclaimed and recycled to the initial Coal-water slurry, so that the water is conserved and residual organic matter can be returned to the gasifier for further treatment.)
Description and Background: This invention relates to the drying and gasification of carbonaceous solids and is particularly concerned with drying an aqueous slurry of coal and the subsequent gasification of the dried coal.
Run-of-mine coal or similar carbonaceous solids will normally contain from about 5 to about 40 weight percent moisture depending upon the type of coal and the geographical area from which it is mined. It is normally desirable to remove this moisture or dry the solids before they are used as fuel to generate steam or otherwise produce heat, or before the solids are used as a feed to liquefaction, gasification, pyrolysis and similar processes wherein the carbonaceous feed material is converted into synthetic liquids and/or gases.
Conventional methods for drying coal normally consist of contacting the coal or similar carbonaceous solids with a hot gas to vaporize the water thereby converting it to steam, which is ordinarily vented to the atmosphere.
Since the resultant steam is vented to the atmosphere, the energy used to heat the gas is wasted and the drying process is inefficient. In some cases the gas used to dry the coal will be a flue gas produced by combusting a gaseous, liquid or solid fuel. If a flue gas is utilized to vaporize the water, it may contain undesirable constituents such as sulfur dioxide produced when the fuel is combusted and expensive scrubbing equipment may be needed to treat the flue gas after it has contacted the coal in order to prevent undesirable atmospheric emissions.
The inefficiency of drying coal and similar carbonaceous solids becomes more severe in catalytic gasification processes where the coal is impregnated with a catalytically active material prior to injection into the gasifier. The impregnation is normally carried out by mixing the coal with an aqueous solution of the catalyst and the resultant mixture is then dried. In such cases large amounts of heat are required to vaporize the water in the mixture and the resultant steam is vented to the atmosphere and its heat energy lost to the process. In noncatalytic gasification processes, it may be desirable to slurry the feed coal with water, pump the entire slurry to gasifier operating pressure and inject it into the gasifier thereby avoiding the use of complex lock-hopper systems to pressurize dry solids. Heat inefficiency, however, is still a problem in this method since the energy that would normally be utilized to dry the slurry prior to injection into the gasifier must now be supplied directly to the gasifier.
In both catalytic and noncatalytic gasification processes where coal is reacted with excess steam, the resultant raw product gas will contain unreacted steam which must be condensed and removed before the product gas is subjected to further processing. The condensed steam is sour water and contains hydrogen sulfide, ammonia and other impurities that are produced during the gasification step. This sour water must be stripped to remove a portion of these impurities and the stripped sour water then sent to wastewater treatment facilities to further purify the water before it can be reused or placed into the environment. These stripping and wastewater treatment steps are quite costly but are required in almost all steam gasification processes.
Summary: In accordance with the invention, it has now been found that an aqueous slurry of carbonaceous solids can be effectively dried while at the same time recovering and utilizing the heat energy required in the drying step by contacting the aqueous slurry of carbonaceous solids with superheated steam in a drying zone maintained at an elevated temperature and pressure. The superheated steam is maintained at a temperature sufficiently higher than the temperature in the drying zone to convert more than 80 weight percent, preferably more than about 90 weight percent of the water in the slurry into steam. Carbonaceous solids of reduced water content are withdrawn at an elevated temperature and pressure from the drying zone and passed to a steam gasification zone where they are gasified with at least a portion of the steam produced in and withdrawn from the drying zone. By using the steam generated in the drying zone to gasify the carbonaceous solids, the energy used to dry the solids is not lost to the overall process but is used in an efficient and advantageous manner.
Since the dried solids removed from the drying zone are at an elevated temperature and pressure, they are particularly suited as feed to a pressurized, high temperature gasification zone.
(The) process of the invention provides a method for drying a slurry of carbonaceous solids in which the energy utilized for drying is recovered in the form of useful high temperature and high pressure steam. As a result, the subsequent use of the recovered steam to gasify the dried solids efficiently utilizes the energy required in the drying step."
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Thus, through a rather logical system of internal recycling, more of the initial Carbon content of the Coal is gasified, forming a synthesis gas for an overall process "wherein the carbonaceous feed material is", via an intermediate synthesis gas, ultimately, "converted into synthetic liquids and/or gases".
And, not only is the Carbon conserved, but, so, through the recovery and reuse of the "high temperature and high pressure steam", so is the internally-generated heat energy.
Our read of the full Disclosure suggests that only nominal amounts of Carbon Dioxide would be produced in the total gasification scheme; amounts or percentages small enough that it might not be an issue. Should we have misread the details, however, we remind you, that, as we've documented, for just one instance in:
Conoco Converts CO2 to Methanol and Dimethyl Ether | Research & Development; concerning: "United States Patent 6,664,207 - Catalyst for Converting Carbon Dioxide to Oxygenates; 2003; Assignee: ConocoPhillips Company; Abstract: A catalyst and process for converting carbon dioxide into ... methanol and dimethyl ether";.
there are catalysts that will convert the Carbon Dioxide contained in a stream of synthesis gas into hydrocarbons; and, as we documented in:
GE and USDOE Harvest CO2 for Hydrocarbon Synthesis | Research & Development; which contains, among other items, additional information concerning: "United States Patent Application 20070149392 - Reactor for Carbon Dioxide Capture and Conversion; 2007; General Electric Company; Abstract: Disclosed herein is a multifunctional catalyst system ... wherein the first catalyst initiates or facilitates the reduction of carbon dioxide to carbon monoxide while the second catalyst initiates or facilitates the conversion of carbon monoxide to an organic compound. Disclosed herein is a method comprising reducing carbon dioxide to carbon monoxide in a first reaction catalyzed by a first catalyst; and reacting carbon monoxide with hydrogen in a second reaction catalyzed by second catalyst; wherein the first catalyst and the second catalyst are disposed upon a single substrate";
there are other catalysts capable of chemically reducing Carbon Dioxide in a synthesis gas stream into more Carbon Monoxide, which catalysts can be combined with other catalysts that facilitate the "easier" reaction between Carbon Monoxide and Hydrogen to form hydrocarbons; in effect, "cleaning up" a synthesis gas stream, as might be generated with such high energy and Carbon efficiency by the process of our subject herein, "United States Patent 4,284,416 - Integrated Coal Drying and Steam Gasification Process".
Finally, a close read of the full Disclosure of "United States Patent 4,284,416" suggests that there might, but only might, it genuinely isn't that clear to us, be some residual "Char", or Carbon, still left behind after all is said and done, even though the complete system does seem so efficient.
If so, we submit that the primarily mineral residue of the gasification and conversion process could be sent on to yet another Exxon-developed technology, as described in our report of:
Exxon Converts Coal Conversion Residues to Cement | Research & Development; concerning: "United States Patent 4,260,421 - Cement Production from Coal Conversion Residues; 1981; Assignee: Exxon Research and Engineering Company; Abstract: Cement is produced by feeding residue solids containing carbonaceous material and ash constituents obtained from converting a carbonaceous feed material into liquids and/or gases into a cement-making zone and burning the carbon in the residue solids to supply at least a portion of the energy required to convert the solids into cement";
wherein any "carbonaceous material", Char, still remaining could be utilized to help convert the mineral residue into an environmentally friendlier substitute for Portland Cement.