The technologies which exist for converting our abundant Coal into more versatile liquid and gaseous hydrocarbons have been around so long, unbeknownst to the majority of those of us resident in US Coal Country, that a great deal of effort has been applied by practitioners of Coal conversion art to the productive disposal and utilization of wastes that might be generated by such processes.
We've documented, and will further document, the use of Coal ash, as might be co-produced by the use of Coal for generating electricity, as an additive, or even a nearly-complete replacement, for the mineral constituents of conventional cement compositions and concrete, as, for just one instance, in:
Scientists Convert Coal Ash to Cement | Research & Development; concerning: "United States Patent Application 0,100,071,597 - Fly Ash-Based Lightweight Cementitious Composition; 2010; United States Gypsum Company; Abstract: A method of making a rapid setting lightweight cementitious composition with improved compressive strength for products such as boards is disclosed. The method mixes fly ash, alkali metal salt of citric acid and lightweight aggregate with water (and) wherein the reactive powder comprises 88.5 to 100% fly ash".
We'll be making report of additional such uses for Coal fly ash in coming days, but, the technologies for converting Coal, either directly, through various solvation processes, or indirectly, through an initial gasification, into gaseous and liquid hydrocarbons, don't, in most cases, unlike more modern Coal combustion processes for power generation purposes, because of the ways in which the reactions must be tailored in order to produce hydrocarbon synthesis raw materials, fully consume and utilize the Carbon content in the Coal fed to the conversion process.
That fact has been recognized and dealt with primarily by developing follow-on processes to the initial gasification or direct liquefaction which in some way extract and further convert the residual Carbon.
We've documented a number of such technologies, as in, for just a few examples, our reports of:
Mobil Oil Converts CoalTL Residues to Hydrocarbon Syngas | Research & Development; concerning: "United States Patent 4,583,993 - Carbon Monoxide and Hydrogen from Carbonaceous Material; 1986; Mobil Oil Corporation; Abstract: Hydrogen and carbon monoxide are produced from (a) product selected from the group consisting of ... char product of coal solvation (and) char product of coal volatilization"; and:
Exxon 1997 Coal Liquefaction Residue Steam-Gasification | Research & Development; concerning: "United States Patent 4,060,478 - Coal Liquefaction Bottoms Conversion by Gasification; 1977; Exxon Research and Engineering Company; Abstract: Heavy bottoms produced by the liquefaction of coal ... are converted into more valuable products by ... (after initially producing) gases, hydrocarbon liquids and ...char, thereafter gasifying the char with steam."
And, once such secondary Carbon recovery processes have been effected, what remains would be a nearly Carbon-free ash which, as in the US Gypsum Company technology cited above, could be used like power plant fly ash in various cement compositions.
We'll be further documenting the potentials for using Coal combustion ash in the manufacture of cement in some reports to follow in the near future, but, herein, we see that the petroleum industry has recognized the potentials for utilizing primary Coal conversion residues for that purpose without, as in the United States Patents "4,583,993" and "4,060,478" cited above, first extracting the residual Carbon content.
What the majority of the public not involved in the making of cement might not fully realize, is that cement making is actually a very energy-intensive process. It takes a lot of heat to calcine the limestone, which calcination, by the way, as we've previously documented, drives off truly prodigious quantities of Carbon Dioxide from the limestone, no matter what the source of heat used for the calcination.
But, the source of heat utilized in cement making is usually the combustion of one sort of fuel or another, and, herein, Exxon proposes using not only the mineral content of Coal conversion residues as raw material for the making of cement, but, as well, their residual Carbon content for at least some of the needed fuel.
Comment concerning the potential relative value of that follows excerpts from the initial link above to:
"United States Patent 4,260,421 - Cement Production from Coal Conversion Residues
Date: April, 1981
Inventors: Leo Brown, et. al., Texas
Assignee: Exxon Research and Engineering Company, New Jersey
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.
Claims: A process for the manufacture of cement which comprises: passing residue solids containing between about 20 weight percent and about 60 weight percent carbonaceous material with the remainder of said residue solids being inorganic ash constituents including calcium silicates and calcium aluminosilicates into a cement-making zone, said residue solids produced by (1) converting a solid carbonaceous feed material in the presence of an alkali metal-containing catalyst into liquids and/or gases thereby producing particles containing carbonaceous material, inorganic ash constituents and alkali metal residues and (2) treating said particles with a calcium-containing compound in the presence of water at a temperature between about 250F. and about 700F. to convert water-insoluble alkali metal constituents in said alkali metal residues into water-soluble alkali metal constituents;
(And:) combusting said carbonaceous material in said residue solids to supply at least a portion of the energy required to convert said residue solids into cement in said cement-making zone and wherein the presence of said calcium silicates and said calcium aluminosilicates decreases the amount of energy required to convert said residue solids into cement.
A process ... wherein said carbonaceous feed material is converted into liquids by liquefaction.
A process ... wherein said solid carbonaceous feed material comprises coal.
A process ... wherein said carbonaceous feed material is converted by gasification in the presence of a potassium-containing catalyst.
A process ... wherein said calcium-containing compound comprises calcium oxide.
(Note: Depending on the grade of raw Coal utilized, "calcium oxide" can be a common ingredient of Coal combustion and Coal gasification ash.)
A process ... wherein said residue solids are contacted with water to remove water-soluble alkali metal constituents prior to passing said solids into said cement-making zone.
(Note: For more info on "potassium-containing" and "water-soluble alkali metal" Coal gasification catalysts, and how they can, as above, be economically recovered and reused, see:
Exxon Recovers and Recycles Coal Conversion Catalyst | Research & Development; concerning: "United States Patent 4,157,246 - Hydrothermal Alkali Metal Catalyst Recovery Process; 1979; 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.")
A process ... wherein said residue solids containing said carbonaceous material and said inorganic ash constituents are mixed with supplementary calcium and silica prior to their introduction into said cement-making zone.
A process ... wherein the carbonaceous content of said residues solids is sufficient to provide substantially all of the energy required to convert said solids into cement.
(And, immediately above, there you have the fuel recovery we alluded to in our introductory comments.)
Background: This invention relates to the production of cement and is particularly concerned with using spent solids produced during coal gasification and similar coal conversion operations to manufacture cement.
Catalytic and noncatalytic coal gasification processes and similar operations carried out at high temperatures generally result in the formation of chars. The chars normally include unconverted carbonaceous constituents of the coal or other feed material and various inorganic constituents generally referred to as ash. It is generally advisable to withdraw a portion of the char from the reaction zone during gasification and similar operations in order to eliminate the ash and prevent it from building up within the reaction zone or other vessels in the system. The amount of char removed will normally be quite large, over 20 weight percent of the feed in some instances, and therefore creates disposal problems.
In gasification and similar processes carried out in the presence of an alkali metal-containing catalyst, the resultant chars will contain alkali metal residues along with unconverted carbonaceous constituents and ash. In order to maintain catalyst cost at a reasonable level, it is essential that the alkali metal constituents be recovered from the char residue and reused in the process. There have been proposals for the recovery of alkali metal constituents by water leaching the char after it is withdrawn from the reaction zone and before it is sent to disposal.
(As in the above-cited process in our previous report concerning: "United States Patent 4,157,246".)
Such a procedure, however, only recovers the water-soluble alkali metal constituents. It has recently been found that increased amounts of alkali metal constituents can be effectively recovered from the char particles by treating the particles with calcium hydroxide in the presence of water at elevated temperatures and pressures. The calcium ions from the calcium hydroxide evidently react with the alkali metal aluminosilicates and other water-insoluble alkali metal compounds in the char particles thereby liberating alkali metal constituents which dissolve in the water to form an aqueous solution which is recycled to the reaction zone.
The spent solids resulting from this treatment step must then be disposed of ... .
(This, is, thus, a process for utilizing the residuals after the catalysts have been recovered.)
(But,) spent solids containing carbonaceous material, ash and other constituents will remain after the catalyst recovery step and must be disposed of in a fashion similar to those produced in noncatalytic processes which do not employ catalyst recovery steps. Normally, the spent solids referred to above are transported from the process site to a dump area where they are used as landfill. Disposal in this manner is expensive since the quantity of the spent residue solids will be relatively large, and therefore transportation and other logistics will be complicated. Moreover, the composition of the residue solids may pose environmental problems that could add considerably to the cost of disposal. Thus, disposal of the waste solids is a significant factor in determining the overall cost of the conversion process and no benefit is gained by throwing away these materials, especially in view of the fact that the energy content of the carbon present is lost to the process.
Summary: The present invention provides a process for the manufacture of cement which at least in part alleviates the difficulties described above. In accordance with the invention, it has now been found that the spent solids containing carbonaceous material, ash and other constituents that are produced during coal gasification and similar conversion processes can be effectively disposed of while at the same time producing a valuable by-product by using the solids as feed to a cement-making process.
Such solids are especially suited as cement-forming materials since they will normally contain calcareous, siliceous and argillaceous materials in addition to relatively large amounts of unconverted carbonaceous material which is burned in the cement-making zone to supply at least a portion of the energy required to convert the solids into cement. The solids will normally contain greater than about 10 weight percent carbonaceous material on a dry basis ... (and, in) some cases the carbonaceous content may be large enough to supply substantially all of the energy required to convert the solids into cement without the need to add an external carbon source for use as fuel.
Although the process of the invention is applicable to any residue solids containing carbonaceous material and ash constituents produced during a process in which a feed material is converted into gaseous and/or liquid products, the process is particularly applicable to conversion residues which contain a relatively large amount of calcium. A large amount of calcium may be present because the feed material is a low rank coal which naturally contains calcium, the conversion process is carried out in the presence of an added calcium-containing material which serves as a catalyst, or the spent solids from the conversion process are treated with a calcium-containing compound to facilitate the recovery of catalyst constituents.
The latter case will exist when a carbonaceous feed material is gasified in the presence of an alkali metal-containing catalyst and the spent solids containing carbonaceous material, ash constituents and alkali metal residues are treated with calcium hydroxide in the presence of water at temperatures between about 250 and 700F. to convert the water-insoluble alkali metal constituents into water-soluble alkali metal constituents, which are recovered and reused as catalyst constituents in the gasification process.
The residue solids exiting this treatment step will contain carbonaceous material, calcium-containing inorganic constituents and other inorganic compounds and are particularly suited for use as feed to a cement-making process since they contain calcium silicates and calcium aluminosilicates and therefore less energy is required to convert these solids to cement than would be required with conventional cement feedstocks such as limestone and sand."
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And, thus, the by-product ash of a Coal conversion process is already "pre-calcined", so to speak, and can consequently reduce cost, by requiring "less energy", through its use in the making of cement.
Furthermore, far more energy would be saved, overall, than is indicated; since, in addition to the fact that the Coal conversion residues have been "pre-calcined", there would be no need, or a reduced need, to expend energy in the mining and transport of the "conventional cement feedstocks such as limestone and sand".
The energy expended for obtaining the raw materials would, in the first place, thus be entirely eliminated.
That, in addition to the reduction in energy needed to then transform the Coal conversion by-products into cement, relative the traditional raw materials.
And, we submit, that would be a somewhat hidden economy in the synthesis of hydrocarbon fuels from Coal, which makes the ultimate cost of such Coal-based fuels, to our total economy, much less than what they might otherwise appear to be.
In that way, it would complement huge savings to our national domestic economy devolving from the use of domestic Coal-based liquid fuels, as we've documented and indicated previously in:
The Real Price of Gasoline | Research & Development; concerning: "An Analysis of the Hidden External Costs Consumers Pay To Fuel Their Automobiles"; and:
Coal TL vs. Hidden Oil Costs | Research & Development; concerning: "NDCF report: the hidden cost of imported oil. The National Defense Council Foundation, an Alexandria, Virginia-based research and educational institution has completed its year-long analysis of the "hidden cost" of imported oil. The NDCF project represents the most comprehensive investigation of the military and economic penalty our undue dependence on imported oil exacts from the U.S. economy"; and:
Actual Costs of Oil | Research & Development; wherein we're told, that: "the International Center for Technology Assessment (CTA) calculates that the actual cost of a gallon of gas to the American consumer could be as high as $15".
Further: Since using the by-products of converting our abundant domestic Coal into hydrocarbons, as via our subject process of "United States Patent 4,260,421", to make Cement, would also - - if Coal conversion and Cement making were to be accounted together, in total, as opposed to separately, in terms of Carbon Dioxide emissions - - enable not only reductions in the potential costs of waste disposal for the Coal conversion process itself, but, as well, rather immense reductions in total, overall CO2 emissions, how is this something, in terms of both our economy and our environment, we can afford to continue not doing?