Claims
- 1. A process for reducing the sulfur content and ash content of a feed coal containing sulfur and mineral matter, the processing comprising the steps of:
- (a) treating the feed coal in a reaction zone with fused alkali-metal caustic at an elevated temperature to remove mineral matter and sulfur from the feed coal, yielding a caustic-treated coal containing chemically bound alkali;
- (b) subsequent to step (a), washing the caustic-treated coal with water to yield water-washed coal and a caustic-rich water;
- (c) subsequent to step (b), washing the water-washed coal with carbonic acid for releasing chemically bound alkali from the water-washed coal to yield carbonic acid-washed coal and an alkali metal carbonate solution; and
- (d) subsequent to step (c), washing the carbonic acid-washed coal with an acid stronger than the carbonic acid to yield (i) product coal having a sulfur content lower than the sulfur content of the feed coal and an ash content lower than the ash content of the feed coal, and (ii) spent acid.
- 2. The process of claim 1 wherein the temperature in the reaction zone is from about 280.degree. to about 400.degree. C.
- 3. The process of claim 1 wherein the caustic is selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof.
- 4. The process of claim 1 wherein the feed coal is treated with sufficient fused alkali-metal caustic to form a free flowing slurry of coal and caustic.
- 5. The process of claim 1 wherein the ratio of caustic to feed coal is from about 2 to about 20 parts by weight caustic per part of coal.
- 6. The process of claim 1 in which the caustic treated coal is washed with sufficient water such that the water washed coal contains less than about 5% by weight free caustic.
- 7. The process of claim 1 in which the water-washed coal is washed with sufficient carbonic acid such that the carbonic acid-washed coal contains substantially no free caustic and less than about 1.5% by weight bound alkali.
- 8. The process of claim 1 wherein the water-washed coal is washed with sufficient carbonic acid such that the combination of coal and carbonic acid has a pH of less than about 6, and the carbonic acid-washed coal contains less than about 0.5% by weight bound alkali.
- 9. The process of claim 1 wherein the feed coal has an ash content of greater than about 6% by weight and a sulfur content of greater than about 2% by weight, and wherein the product coal has an ash content of less than about 0.1% by weight and a sulfur content of less than about 0.5% by weight.
- 10. A process for reducing the sulfur content and ash content of a feed coal containing sulfur and mineral matter, the process comprising the steps of:
- (a) treating the feed coal in a reaction zone to remove fused alkali metal caustic at an elevated temperature to remove mineral matter and sulfur from the feed coal, yielding a caustic-treated coal containing chemically bound alkali;
- (b) subsequent to step (a), washing the caustic-treated coal with water to yield water-washed coal and a caustic-rich water;
- (c) subsequent to step (b), washing the water-washed coal with carbonic acid for releasing chemically bound alkali from the water-washed coal to yield carbonic acid-washed coal and a carbonate solution comprising alkali metal carbonates and bicarbonates;
- (d) subsequent to step (c), washing the carbonic acid-washed coal with an acid stronger than the carbonic acid to yield (i) product coal having a sulfur content lower than the sulfur content of the feed coal and an ash content lower than the ash content of the feed coal, and (ii) spent acid;
- (e) recovering substantially anhydrous alkali metal caustic by the steps of:
- (i) treating the carbonate solution with lime in a caustic regeneration zone to give a dilute aqueous caustic and a calcium carbonate precipitate;
- (ii) separating the dilute aqueous caustic from the precipitate;
- (iii) removing substantially all of the water from the dilute aqueous caustic to recover substantially anhydrous alkali metal caustic; and
- (f) recycling the recovered alkali metal caustic to the reaction zone.
- 11. The process of claim 10 in which the step of washing the caustic-treated coal with water comprises washing with water removed from the dilute aqueous caustic.
- 12. The process of claim 9 in which the step of washing the water-washed coal with carbonic acid comprises forming carbonic acid with water removed from the dilute aqueous caustic.
- 13. The process of claim 10 comprising the additional step of heating the precipitated calcium carbonate in a lime recovery zone to produce lime and carbon dioxide.
- 14. The process of claim 13 in which the step of washing the water-washed coal with carbonic acid comprises forming carbonic acid with the carbon dioxide produced in the lime recovery zone.
- 15. The process of claim 14 in which the step of treating the carbonate solution with lime comprises treating the carbonate solution with the lime produced in the lime recovery zone.
- 16. The process of claim 10 wherein the step of treating feed coal with fused alkali metal caustic yields a mixture of the caustic-treated coal and a spent fused caustic containing sulfur and mineral matter removed from the coal, the process further comprising the steps of:
- (a) separating at least a portion of the spent fused caustic from the caustic-treated coal; and
- (b) recycling the separated spent fused caustic to the reaction zone.
- 17. The process of claim 16 wherein substantially all fused alkali metal caustic present in the mixture of the caustic-treated coal and spent fused coal is recycled to the reaction zone in the (a) separated spent fused caustic and (b) the recovered alkali metal caustic.
- 18. The process of claim 16 wherein the feed coal is treated with sufficient fused alkali metal caustic to form a free flowing slurry of coal and caustic.
- 19. The process of claim 16 wherein the ratio of caustic to feed coal in the reaction zone is from about 2 to about 20 parts by weight caustic per part of coal.
- 20. The process of claim 16 wherein the recycled spent fused caustic has a sulfur content of less than about 2% by weight sulfur and less than about 5% by weight mineral matter.
- 21. A process for reducing the sulfur content and ash content of a feed coal containing sulfur and mineral matter, the process comprising the steps of:
- (a) treating the feed coal in a reaction zone with fused alkali metal caustic at an elevated temperature to remove mineral matter and sulfur from the feed coal, yielding a caustic-treated coal containing chemically bound alkali;
- (b) subsequent to step (a), washing the caustic-treated coal with water to yield water washed coal and a caustic-rich water containing sulfur compounds and mineral matter;
- (c) subsequent to step (b), washing the water-washed coal with carbonic acid for releasing chemically bound alkali from the water-washed coal to yield carbonic acid-washed coal and a first carbonate solution comprising alkali metal carbonates and bicarbonates;
- (d) subsequent to step (c), washing the carbonic acid-washed coal with an acid stronger than the carbonic acid to yield (i) product coal having a sulfur content lower than the sulfur content of the feed coal and an ash content lower than the ash content of the feed coal, and (ii) spent acid;
- (e) recovering substantially anhydrous alkali metal caustic by the steps of:
- (i) cooling the caustic-rich water to yield (A) a first precipitate comprising alkali metal sulfides and mineral matter, and (B) concentrated aqueous caustic; and
- (ii) removing the water from the concentrated aqueous caustic to recover substantially anhydrous alkali metal caustic; and
- (f) recycling the recovered alkali metal caustic to the reaction zone.
- 22. The process of claim 21 further comprising the recovery of addition alkali metal caustic by the steps of:
- (a) treating the first carbonate solution with lime in a caustic regeneration zone to give a first dilute aqueous caustic, and a second precipitate- comprising calcium carbonate;
- (b) separating the first dilute aqueous caustic from the second precipitate;
- (c) removing the water from the first dilute aqueous caustic to recover additional substantially anhydrous alkali metal caustic; and
- (d) recycling the additional alkali metal caustic recovered from the first dilute aqueous caustic to the reaction zone.
- 23. The process of claim 22 further comprising the recovery of additional alkali metal caustic by the steps of:
- (a) contacting the first precipitate with water to give (i) an alkali metal sulfide solution, and (ii) solid mineral matter;
- (b) treating the alkali metal sulfide solution with carbon dioxide to give hydrogen sulfide gas and a second carbonate solution comprising alkali metal carbonates and bicarbonates;
- (c) treating the second carbonate solution with lime in caustic regeneration zone to give a second dilute aqueous caustic, and a third precipitate comprising calcium carbonate;
- (d) separating the second dilute caustic from the third precipitate;
- (e) removing the water from the second dilute aqueous caustic to yield additional substantially anhydrous alkali metal caustic; and (f) recycling the additional alkali metal caustic recovered from the second dilute caustic to the reaction zone.
- 24. The process of claim 23 wherein lime is regenerated for reuse by heating the precipitated calcium carbonate in a lime recovery zone to produce lime and carbon dioxide.
- 25. The process of claim 23 wherein at least part of the carbon dioxide produced in the lime recovery zone is used for treating the alkali metal sulfide solution.
- 26. The process of claim 23 wherein the hydrogen sulfide gas is used to form sulfuric acid which is used for washing the carbonic acid-washed coal.
- 27. The process of claim 26 wherein the spent acid is neutralized with lime to give waste water containing dissolved alkali metal sulfates and insoluble calcium sulfate.
- 28. A process for upgrading a feed coal, which has been physically cleaned and which has a mineral matter content of greater than about 6% by weight and a sulfur content of greater than about 2% by weight, to produce a product coal with an ash content of less than 0.1% by weight of a sulfur content of less than about 0.5% by weight, the process comprising the steps of:
- (a) contacting feed coal in a reaction zone with fused alkali metal caustic at a temperature of from about 325.degree. to 375.degree. C. and substantially atmospheric pressure to remove sulfur and mineral matter from the feed coal, yielding caustic-treated coal containing chemically bound alkali, the caustic being selected from the group consisting of sodium hydroxide, potassium hydroxide, and mixtures thereof, the mass ratio of fused alkali metal caustic to coal being from about 2:1 to about 20:1;
- (b) subsequent to step (a), washing the caustic-treated coal with sufficient water to yield:
- (i) a water-washed coal containing less than about 5% by weight free caustic, and
- (ii) a caustic-rich water containing sulfur and mineral matter and having an alkali metal hydroxide concentration of from about 40 to about 50% by weight;
- (c) subsequent to step (b), contacting the water-washed coal with sufficient carbonic acid to from a coal/carbonic acid mixture with a pH of less than about 6 for releasing chemically bound alkali from the water-washed coal, then separating the mixture to give:
- (i) a carbonic acid-washed coal containing substantially no free caustic and less than about 0.5% by weight bound alkali and
- (ii) a first carbonate solution containing alkali metal carbonates and bicarbonates;
- (d) subsequent to step (c), washing the carbonic acid-washed coal with sulfuric acid having a pH of less than about 2 to give product coal and spent sulfuric acid;
- (e) recovering anhydrous alkali metal caustic for recycle to the reaction zone by the steps of:
- (i) cooling the caustic-rich water to yield (A) a first precipitate comprising alkali metal sulfides and mineral matter and (B) a concentrated aqueous caustic,
- (ii) contacting the first precipitate with water to give an alkali metal sulfide solution and solid mineral matter,
- (iii) treating the alkali metal sulfide solution with carbon dioxide in a sulfide reaction zone to give hydrogen sulfide and a second carbonate solution comprising alkali metal carbonates and bicarbonates,
- (iv) treating the first and the second carbonate solutions with lime in a caustic regeneration zone to give a dilute aqueous caustic and a second precipitate comprising calcium carbonate,
- (v) removing the water from the concentrated and dilute aqueous caustics to recover anhydrous alkali metal caustic,
- (vi) recycling the recovered anhydrous alkali metal caustic to the reaction zone;
- (f) regenerating the lime by heating the second precipitates in a lime recovery zone to produce lime and carbon dioxide;
- (g) forming the carbonic acid for washing the water washed coal and to treat the alkali metal sulfide solution with carbon dioxide produced in the lime recovery zone;
- (h) producing the sulfuric acid used to wash the carbonic acid-washed coal with hydrogen sulfide produced in the sulfide reaction zone; and
- (i) neutralizing the spent sulfuric acid with lime to give waste water containing alkali metal sulfates and insoluble calcium sulfate.
- 29. The process of claim 28, wherein the step of contacting feed coal with fused alkali metal caustic yields a mixture of the caustic-treated coal and a spent fused caustic containing sulfur and mineral matter removed from the coal, the process further comprising the steps of:
- (a) separating at least a portion of the spent fused caustic from the caustic-treated coal; and
- (b) recycling the separated spent fused caustic to the reaction zone;
- wherein the recycled spent fused caustic comprises less than about 2% by weight sulfur and less than about 5% by weight mineral matter.
- 30. The process of claim 29 wherein substantially all of the caustic in the mixture of the caustic-treated coal and spent fused caustic is recycled to the reaction zone in (a) separated spent fused caustic and (b) recovered anhydrous alkali metal caustic.
- 31. The process of claim 1, 10, 21, or 28 wherein the step of washing the caustic-treated coal with water comprises washing the coal in a countercurrent staged system comprising a plurality of stages, including at least one intermediate stage wherein each intermediate stage comprises the steps of:
- (i) slurrying the coal with water,
- (ii) separating the slurry into wet coal and a liquid, and
- (iii) sending the wet coal to the following stage and the liquid to the prior stage.
- 32. A process for reducing the sulfur content and ash content of a feed coal containing sulfur and mineral matter, the process comprising the steps of:
- (a) treating feed coal in a reaction zone with fused alkali-metal caustic at an elevated temperature to remove mineral matter and sulfur from the feed coal, yielding a caustic-treated coal containing chemically bound alkali;
- (b) subsequent to step (a), washing the caustic-treated coal with water to yield water-washed coal and a caustic-rich water in a countercurrent staged water-washed system containing a plurality of stages, including at least one intermediate stage wherein each intermediate stage comprises the steps of:
- (i) slurrying the coal with water,
- (ii) separating the slurry into wet coal and a liquid, and
- (iii) send the wet coal to the following stage and the liquid to the prior stage; and
- (c) subsequent to step (b), washing the water-washed coal with an acid to yield (i) product coal having a sulfur content lower than the sulfur content of the feed coal and an ash content lower than the ash content of the feed coal, and (ii) spent acid.
RELATED APPLICATIONS
This application is a continuation of application Ser. No. 770,324, filed Aug. 27, 1985, now abandoned, which is a continuation-in-part of U.S. Patent Application Ser. No. 486,276 filed on Mar. 10, 1983 by Robert Meyers and Walter D. Hart, now U.S. Pat. No. 4,545,891 issued on Oct. 8, 1985; which is based on an International Application filed under the Patent Cooperation Treaty, application No. PCT/US82/00394 filed on Mar. 30, 1982, published on Oct. 14, 1982, Publication No. WO82/03404; which is based, as a continuation-in-part, on U.S. Application Ser. No. 349,514 filed on Mar. 31, 1981 now U.S. Pat. No. 4,445,756. These applications are incorporated herein by this 1 reference.
US Referenced Citations (69)
Non-Patent Literature Citations (4)
Entry |
Coal Desulfurization, R. A. Meyers, 1977, pp. 25-54, 201-209, 230-4. |
"Conversion of coal to simple compounds", Parker et al. Industrial & Engr. Chem., vol. 47, No. 6, Aug., 1955, pp. 1586-1592. |
The effect of molten caustic on Pyritic Sulphur in Bituminous Coal, Masciantonio, pp. 269-275. |
Masciantonio, "The Effect of Molten Caustic on Pyritic Sulphur in Bituminous Coal"275. Applied Research Laboratory United States Steel Corp. (1904) pp. 269 |
Continuations (1)
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770324 |
Aug 1985 |
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Continuation in Parts (2)
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486976 |
Mar 1983 |
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349514 |
Mar 1981 |
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