Claims
- 1. A process for producing a coal product from coal and coal derivatives, said coal product having a mineral matter content of less than about 5 percent by weight comprising the steps of:
- (a) contacting coal of a size less than about an inch with an aqueous HF acid leach to solubilize at least a portion of said mineral matter;
- (b) separating the spent HF leachate and impurities dissolved therein from the coal;
- (c) contacting said coal from step (b) with an aqueous HCl acid leach;
- (d) separating the spent HCl leachate and the impurities dissolved therein from the coal;
- (e) removing pyrite from said leached coal to produce a coal product substantially free of pyrite;
- (f) treating said coal product to remove any halogens present as volatile halides;
- (g) regenerating acids by contacting said acid leachate in the presence of added SO.sub.2 and oxygen with water vapor under reaction conditions selected to regenerate an acid selected from the group consisting of HF and HCl and to form a residue comprising the oxides of Al and Fe and the sulfates of one or more of the group consisting of Ca, K, and Na; and
- (h) recycling said regenerated acids to the respective leaches.
- 2. A process according to claim 1 wherein said coal is comminuted to a size less than about 5 mm.
- 3. A process according to claim 2 wherein said coal is comminuted to a size less than 1/2 mm.
- 4. A process according to claim 1 further comprising pre-leaching said coal with a hydrochloric acid leach wherein said acid leach comprises from about 1 to about 20 percent by weight hydrochloric acid; and wherein said hydrochloric acid leach is at a temperature of about 40.degree. C. to form a pre-leached coal and a spent HCl leach liquor.
- 5. A process according to claim 4 wherein said spent HCl leach liquor and said pre-leach coal are separated.
- 6. A method according to claim 5 wherein said spent HCl leach liquor undergoes pyrohydrolysis to regenerate said HCl acid and wherein said regenerated HCl acid is recycled to the hydrochloric pre-leach step.
- 7. A process according to claim 1 wherein said HF leach is conducted in a two-stage countercurrent leach system.
- 8. A process according to claim 1 wherein the concentration of said HF leach is in the range of from about 5 to about 70 weight percent.
- 9. A process according to claim 8 wherein said concentration of HF leach is in the range of from about 15 to about 30 weight percent.
- 10. A process according to claim 1 wherein the second stage of a countercurrent HF leach is at a concentration of 20 percent HF.
- 11. A process according to claim 1 wherein said HF leach is conducted at a temperature of from about 10.degree. C. to incipient boiling.
- 12. The process according to claim 11 wherein said temperature is at a range of from about 10.degree. to about 40.degree. C.
- 13. A process according to claim 1 wherein said contacting of step (a) is for a time period sufficient to solubilize a substantial amount of the mineral matter and the total time is from about 1/6 to about 8 hours.
- 14. A process according to claim 1 wherein the concentration of said HCl leach is from about 3 to about 38 weight percent HCL and said contacting with HCl leach is for a time period of from about 1/6 to about 4 hours at a temperature of from about 40.degree. to incipient boiling.
- 15. A process according to claim 14 wherein concentration of said HCl acid leach is from about 5 to 15 weight percent HCl and for a time period of from about 1 to about 2 hours and at a temperature range of from about 80.degree. C. to incipient boiling.
- 16. A process according to claim 1 wherein said separated coal of step (b) is washed with water prior to said HCl acid leach.
- 17. A process according to claim 1 wherein said separated coal of step (d) is washed with water prior to said pyrite removal.
- 18. A process according to claim 1 wherein said separation of step (e) is by gravity separation.
- 19. A process according to claim 1 wherein said physical separation of step (e) is magnetic separation.
- 20. A process according to claim 1 wherein said treating of step (f) comprises heating to a temperature of from about 225.degree. C. to about 400.degree. C. for a time sufficient to remove any halogens present in said coal product as volatile halides to an amount below about 1/2 percent by weight.
- 21. A process according to claim 1 wherein said treating of step (f) comprises washing at a temperature less than boiling with a wash selected from the group consisting of water, acetic acid, alcohol, ammonium hydroxide, nitric acid, and mixtures thereof and then heating the coal product to dry it.
- 22. A process according to claim 1 wherein said HF acid leach liquor separated in step (b) contains coal fines and further comprising regenerating said HF leachate in a pyrohydrolyzer fired at least in part by said coal fines.
- 23. A process according to claim 1 in which said contacting of step (c) comprises co-current leaching.
FIELD OF INVENTION
This is a continuation-in-part of U.S. patent application Ser. No. 06/467,382, filed Feb. 17, 1983 now abandoned.
This invention relates to processes for producing environmentally acceptable fuels from coal and, in particular, to hydrometallurgical processes for removing contaminants from coal.
Energy demands by the industrialized world are continuing to rise, while the rate of new oil discoveries is falling. Within the next 30 years, available petroleum supplies will fail to meet demand, and oil will no longer be able to serve as the world's major energy source. Other energy sources such as geothermal, solar, and fusion are unlikely to be sufficiently developed to serve as replacements for oil. Coal, on the other hand, exists in relative abundance in the United States, and if it can be adapted to use in existing plants which have been engineered for petroleum use, it can serve as an inexpensive substitute for, and successor to, the more expensive oil fuels in use today. In order to be used as an oil substitute, however, the coal must be converted to a fluid state, so that systems burning fuel oil, diesel fuel, and other petroleum products can be adapted to its use with minimal equipment modification. The coal must also be cleaned, or purged of its mineral matter (ash precursor) content, to increase fuel value per pound for efficient handling and use; and its sulfur content must be reduced to minimize offgas cleanup, so as to meet environmental pollution standards.
It has been reported that treating raw, lump coal with hydrogen fluoride in liquid or gaseous form removes much of the ash content, and this removal of ash from the interstices within the coal tends to cause the coal to break up, so that the hydrogen fluoride also serves as a comminuting agent to produce coal fines. The coal particles produced, however, are still too large to be used as fluid fuel substitutes. In addition, hydrogen fluoride is an extremely expensive reagent, so that its use is uneconomical unless it can be recycled. The present invention solves these problems by providing an integrated process for the use of hydrogen fluoride to clean coal followed by a sequential HCl acid leaching step. The preferred embodiment of this invention includes separate regeneration schemes for the hydrogen fluoride acid leachate and hydrogen chloride acid leachate for recycle for use in the respective fluid systems. Valuable mineral by-products, such as aluminum and titanium compounds, or compounds of other elements contained in the mineral matter associated with the feed coal, may also be recovered from the process.
The finely-ground, acid-purged coal product is usable not only as a substitute for petroleum fuels, e.g., as a turbine fuel, but also may substitute for activated carbon, or as a feedstock for carbon black, electrode carbon, and various chemical processes.
U.S. Pat. No. 4,169,710 assigned to Chevron describes a process for the use of concentrated hydrogen halide, such as hydrogen fluoride, as a comminuting agent for raw coal. The patent also discloses the use of the hydrogen halide to dissolve and remove ash and sulfur from raw (unground) coal in a single step treatment. It does not provide for a sequential two-acid leach system. This patent also mentions that the hydrogen halide may be purified and recycled; however, no procedure for doing so is disclosed. The Chevron patent does not disclose the use of finely-ground, hydrogen fluoride-purged coal as a substitute for fluid fuels or other forms of finely-divided, highly purified hydrocarbons.
European Patent Application No. 80300800.2, filed Mar. 14, 1980, and published Oct. 1, 1980, under Publication No. 0 016 624, by Kinneret Enterprises, Ltd., discloses a coal de-ashing process utilizing liquid or gaseous hydrogen fluoride to remove silica and/or aluminum bearing mineral matter and other reactive materials from substances, such as coal, which do not react with hydrogen fluoride under the same conditions. The hydrogen fluoride is recovered as a gaseous product at several stages. In the Kinneret process, hydrogen fluoride in gaseous form contacts the coal, which is first ground to -200 mesh. The unreacted gas is then separated by density methods and recycled. An aqueous solution of 20-30% hydrogen fluoride is then used to leach the formed fluoride minerals away from the coal, and hydrogen fluoride gas is recovered from this solution at raised temperatures and pressures, simultaneously causing the crystallization of aluminum, calcium, magnesium, and manganese fluorides. Other minerals including titanium, potassium, and sodium fluorides remain in solution. The heavy gas fraction resulting from the hydrogen fluoride gas treatment of the coal is contacted at elevated temperatures and pressures with water in two subsequent stages to remove sulfur and silicon dioxide and produce gaseous hydrogen fluoride in both cases for recycle. The Kinneret process does not utilize the advantages of an HCl acid leach following the HF treatment. The Kinneret publication discloses the comminution of a coal prior to treating with hydrogen fluoride to remove mineral content, it does not disclose a procedure for producing a finely-ground product suitable as a liquid fuel substitute or other applications as discussed above.
U.S. Pat. No. 4,083,940 to Das discloses the use of a 0.5-10% hydrofluoric acid solution in combination with an oxidizing agent such as nitric acid, to purify coal to electrode purity (0.17% ash). A gaseous oxygen-containing materal is bubbled through the mixture during leaching to provide additional mixing action and oxidation.
U.S. Pat. No. 3,961,030 to Wiewiorowski et al. describes the use of a 10-80% hydrogen fluoride solution to leach clay for the recovery of aluminum. Hydrogen fluoride is recovered for recycle by the addition of water and heat to aluminum fluoride. The recovered hydrogen fluoride can be dissolved in water and recycled in aqueous form.
U.S. Pat. No. 2,808,369 to Hickey describes the treatment of coal with fluoride salts, and with hydrogen fluoride gas, after first heating the coal to effect a partial devolatilization.
U.S. Pat. No. 4,071,328 to Sinke describes the removal of FeS from coal by hydrogenation and contact with aqueous hydrogen fluoride.
U.S. Pat. Nos. 3,870,237 and 3,918,761 to Aldrich disclose the use of moist ammonia for in situ treatment of coal to fragment the coal and facilitate the separation of inorganic components.
U.S. Pat. No. 3,863,846 to Keller, Jr., et al. describes an apparatus and method for the utlization of anhydrous ammonia as a coal comminuting agent.
Bureau of Mines Report of Inventigations No. 5191, "Coal As A Source of Electrode Carbon In Aluminum Production," (February, 1956) at page 7 discloses the use of froth flotation followed by hydrofluoric-hydrochloric acid leaching, using a solution containing 5 parts of the combined acids to 95 parts water. At page 29, the use of a 2.44 Normal solution of hydrofluoric-hydrochloric acid is used to leach coal.
The present invention provides processes for producing a high-purity coal product with less than about 5 weight percent impurities therein in which the coal product is suitable for use as a substitute for petroleum fuels. The processes generally comprise the following steps: (a) contacting coal of a size less than about an inch with an aqueous HF acid leach to solubilize at least a portion of the coal mineral matter; (b) separating the spent HF leach and dissolved impurities therein from the coal; (c) contacting said coal with an aqueous HCl acid leach to solubilize additional coal mineral matter; (d) separating the spent HCl leach and impurities dissolved therein from the coal; (e) separating the pyrite from the coal; (f) washing and drying the coal to remove residual contaminants, including Cl.sup.- and F.sup.- ions; and (g) regenerating the spent acid leach liquor and recycling said acid for use in the respective sequential leaches. In a preferred embodiment, the coal feed material is pre-treated by an HCl acid pre-leach, particularly for coals containing high levels of calcium. In another preferred embodiment, in an alternative or in addition to the washing and drying step, the coal product may be thermally treated to remove low volatile contaminates.
US Referenced Citations (35)
Foreign Referenced Citations (6)
| Number |
Date |
Country |
| 26200 |
Mar 1983 |
AUX |
| 23235 |
Jul 1983 |
AUX |
| 31282 |
Jul 1983 |
AUX |
| 0027493 |
Apr 1981 |
EPX |
| 0016624 |
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Non-Patent Literature Citations (2)
| Entry |
| Bureau of Mines Report of Investigations, No. 5191, "Coal as a Source of Electrode Carbon in Aluminum Production", (Feb. 1956) (p. 7+). |
| Wolfkovich et al., Comptes Rendus (Doklady) De l'Academie des Sciences de L'URSS, 1942, vol. 16, No. 1, pp. 21-23. |
Continuation in Parts (1)
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Number |
Date |
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| Parent |
467382 |
Feb 1983 |
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Patent Grant
4743271
