Claims
- 1. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles in which the slurry is at least 60% water by weight, said method comprising the steps of:
- A. adding a fluid to the aqueous slurry of carbonaceous and non-carbonaceous particles to form a first mixture, in which less than 20% of the combined weight of the fluid and the carbonaceous and non-carbonaceous fine particles is fluid, said fluid being a light hydrocarbon such that it is free-flowing and in a liquid state at temperatures below 20.degree. C., and that it is lyophilic to carbonaceous particles and lyophobic to water and non-carbonaceous particles;
- B. agitating said first mixture to preferentially agglomerate said carbonaceous particles into discrete agglomerates, while the non-carbonaceous particles remain substantially unagglomerated;
- C. separating the discrete agglomerates from said first mixture to form a substantially non-carbonaceous slurry;
- D. adding a flocculant to said non-carbonaceous slurry to form a second mixture, said flocculant being lyophobic to water and lyophilic to non-carbonaceous particles;
- E. removing a precipitate and separating water from said second mixture; and
- F. separating flocculated solids from said precipitate to form a substantially solids-free aqueous solution.
- 2. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 wherein:
- said flocculant has a molecular weight of at least about 100,000.
- 3. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 wherein:
- said flocculant has a molecular weight of at least about 1,000,000.
- 4. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 and further comprising the step of:
- G. recirculating the water separated from said second mixture to a coal washing process.
- 5. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 4 and further comprising the step of:
- H. recirculating said solids-free aqueous solution to said second mixture.
- 6. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 and further comprising the step of:
- G. recirculating said solids-free aqueous solution to said second mixture.
- 7. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 and further comprising the steps of:
- G. adding a binder liquid to the discrete agglomerates to form a third mixture said binder liquid being lyophobic to water and lyophobic to carbonaceous material; and
- H. agitating said third mixture to dewater and pelletize the discrete agglomerates.
- 8. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 and further comprising:
- G. pelletizing the flocculated solids separated from the precipitate.
- 9. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 8 wherein:
- the step G of pelletizing is performed at least partially concurrently with step E of removing a precipitate and with step F of separating flocculated solids said concurrent steps being carred out in a single apparatus.
- 10. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 1 wherein:
- step E of removing a precipitate is performed at least partially concurrently with step F of separating flocculated solids, said concurrent steps being carried out in a single apparatus.
- 11. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles, said method comprising the steps of:
- A. adding an aqueous slurry of carbonaceous and non-carbonaceous particles having a relatively high solids content to an aqueous slurry of carbonaceous and non-carbonaceous particles having a relatively low solids content to form a processable aqueous slurry of carbonaceous and non-carbonaceous particles that is at least 60 percent water by weight;
- B. adding a fluid to the processable aqueous slurry to form a first mixture in which less than 20 percent of the combined weight of the fluid and the carbonaceous and non-carbonaceous particles is fluid, said fluid being a light hydrocarbon such that it is free-flowing and in a liquid state at temperatures below 20.degree. C., and that it is lyophilic to carbonaceous particles and lyophobic to water and non-carbonaceous particles;
- C. agitating said first mixture to preferentially agglomerate said carbonaceous particles into discrete agglomerates while the non-carbonaceous particles remain substantially unagglomerated;
- D. separating the discrete agglomerates from said first mixture to form a substantially non-carbonaceous slurry;
- E. adding a flocculant to said non-carbonaceous slurry to form a second mixture, said flocculant being lyophobic to water and lyophilic to non-carbonaceous particles;
- F. removing a precipitate and separating water from said second mixture; and
- G. separating flocculated solids from said precipitate to form a substantially solids-free aqueous solution.
- 12. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 wherein:
- said flocculant has a molecular weight of at least about 100,000.
- 13. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 wherein:
- said flocculant has a molecular weight of at least about 1,000,000.
- 14. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 and further comprising the step of:
- H. recirculating the water separated from said second mixture to a coal washing process.
- 15. A method for reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 14 and further comprising the step of:
- I. recirculating said solids-free aqueous solution to said second mixture.
- 16. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 and further comprising the step of:
- H. recirculating said solids-free aqueous solution to said second mixture.
- 17. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 and further comprising the steps of:
- H. adding a binder liquid to the discrete agglomerates to form a third mixture, said binder liquid being lyophobic to water and lyophilic to carbonaceous material; and
- I. agitating said third mixture to dewater and pelletize the discrete agglomerates.
- 18. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 and further comprising in addition:
- H. pelletizing the flocculated solid separated from the precipitate.
- 19. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 18 wherein:
- the step H of pelletizing is performed at least partially concurrently with step F of removing a precipitate and with step G of separating flocculated solids said concurrent steps being carried out in a single apparatus.
- 20. A method of reclaiming water and carbonaceous material from an aqueous slurry of carbonaceous and non-carbonaceous particles as set forth in claim 11 wherein:
- Step F of removing a precipitate is performed at least partially concurrently with step G of separating flocculated solids, said concurrent steps being carried out in a single apparatus.
RELATED APPLICATION
This application is a continuation of copending application Ser. No. 115,017, filed Jan. 24, 1980, now abandoned, which in turn is a continuation of application Ser. No. 941,055, filed Sept. 11, 1978, now abandoned, which in turn is a continuation-in-part of application Ser. No. 608,059, filed Aug. 27, 1975, now also abandoned, which in turn is a continuation of application Ser. No. 540,348, filed Jan. 13, 1975, now abandoned.
Mechanized coal preparation plants use large quantities of water to remove coal fines from the coal. The effluent or underflow from the wash treatment typically contains 5 to 15% solids of coal having particle sizes in the range of 150 microns and less (i.e. 100 mesh Tyler sieve). Typically, the underflow is flocculated by addition of, for example, starch or polyacrylamide in a thickener. The solids content of the underflow is increased to typically about 50% in the thickener, and water reclaimed for recirculation to the coal washing plant.
The thickened underflow is then generally pumped to a settling pond where the solids settle out and the reclaimed water is made available for reuse in the coal washer. Such settling ponds are, however, increasingly difficult to construct and maintain. There is often limited land available at the coal washing plant, which requires pumping of the underflow over long distances at substantial cost. Moreover, even where there is land available adjacent the washing plant, environmental laws have made such settling ponds difficult and expensive to construct and operate in compliance with state and federal regulations. And, permanent use of settling ponds presents the problems and costs of disposing of the sediment. In addition, such settling ponds result in loss of the carbonaceous material of coal in the thickened underflow.
Recently, various methods have been proposed for reclaiming coal fines from the underflow. One of these processes is the coal beneficiation process described in U.S. Pat. No. 3,665,066. Instead of flocculation in a thickener, a hydrocarbon such as kerosene or light fuel oil is added to the underflow in amounts typically of about 2 to 10% by weight of the solids in the underflow. The mixture is then agitated by conventional apparatus. The carbonaceous particles, being lyophobic to the water and lyophilic to the hydrocarbon, are preferentially wetted by the hydrocarbon and coalesce into dewatered, coarser agglomerates generally of diameters of up to 1 millimeter, while the other solids (which are lyophilic to water) remain suspended in the water. The carbonaceous agglomerates, in turn, are separated from the water and ash in a conventional separator, e.g. elutriator, cyclone or spiral, and the separated agglomerates pelletized in a balling device using seed particles of coarser coal. The difficulty with this process is that the water still contains roughly 1 to 5% solids, and, therefore, cannot be utilized in the coal washing plant. Generally, the effluent is still discharged to a settling pond. There, the solids are settled out to enable the water to be reused or, alternatively, discharged into rivers and streams in compliance with state and federal environmental regulations.
The present invention overcomes these difficulties and disadvantages of previous water reclaiming techniques. It totally eliminates the need for a settling pond, while reclaiming the water for use in a coal washing plant. Furthermore, it provides a method for reclaiming the carbonaceous material of coal fines from existing settling ponds, while optimizing the reclaimation process and eliminating the environmental and safety hazards of the numerous existing settling ponds.
A method is provided for reclaiming both water and the carbonaceous material of coal from an aqueous slurry of particles of coal that contains both carbonaceous and non-carbonaceous materials. Preferably, the slurry is comprised of at least 60 percent water by weight and the geometric mean particle size of the coal particles in the aqueous slurry is less than 150 microns. A fluid that is lyophobic to water and the non-carbonaceous particle of the coal and lyophilic to the carbonaceous particles of the coal is added to the aqueous slurry to form a first mixture in which less than 20 percent by weight of the fluid and carbonaceous and non-carbonaceous coal particles is fluid. The fluid is such that it is in a free-flowing liquid state at temperatures below 80.degree. C. and, preferably, at temperatures below 20.degree. C. The first mixture is agitated to preferentially agglomerate the carbonaceous particles to form carbonaceous agglomerates while the non-carbonaceous particles remain substantially disposed in the slurry. The carbonaceous agglomerates are then separated from the first mixture to form a substantially non-carbonaceous aqueous slurry substantially free of carbonaceous material and agglomerating fluid.
A flocculant that is lyophobic to water and lyophilic to non-carbonaceous material is then added to the non-carbonaceous aqueous slurry to form a second mixture. The lyophobic flocculant is of a molecular weight greater than 100,000, preferably greater than 1,000,000, and most desirably between 3,000,000 and 15,000,000. Flocculated solids are then precipitated from the second mixture to separate water from the second mixture. Flocculated solids are then separated from the precipitate to form an aqueous solution that is substantially free of solids. Thereafter, the separated flocculated solids preferably are dewatered and pelletized as hereinafter described.
Preferably, the method provides a closed system for a coal washing plant so that only relatively small quantities of additional fresh water are needed for continuous operation of the coal washing plant. In accordance with the preferred method the water separated from the non-coal aqueous slurry is recirculated to the coal washing plant, and, also in accordance with the preferred method the solids-free aqueous solution is recirculated to the second mixture or, alternatively to the coal washing plant. Where the solids-free aqueous solution contains substantial quantities of flocculant, the flocculant is preferably reused in the precipitation step; and the water of the solids-free aqueous solution is clarified and separated from the second during precipitation, and recirculated to the coal washing plant.
Another preferred embodiment involves optimizing the operating efficiency of the method, while reclaiming the carbonaceous material of coal sediment from existing settling ponds. Specifically, while the method is utilizable with slurrys of widely varying solids concentration, generally 5 to 40% solids content and typically 20 to 25% solids content by weight in the slurry is provided for efficient operation. Typically, the aqueous slurry as it comes from a coal washing plant is of relatively low solids content, e.g. 5 to 15%. An aqueous slurry of coal and ash fines having relatively high solids content, i.e. at least about 50% solids by weight, is available from the sediment of existing settling ponds. By mixing the high solids aqueous slurry with the low solids aqueous slurry in the appropriate proportion, the operation of the method can be optimized and the sediment of existing settling ponds can be removed and the carbonaceous material therein reclaimed.
The carbonaceous agglomerates separated from the first mixture may be in certain instances utilized directly in that form. However, the carbonaceous agglomerates are preferably pelletized into larger and denser carbonaceous pellets that are more suitable for general use. The pelletizing may be accomplished by the balling procedure described in U.S. Pat. No. 3,665,066, cited above. Preferably, however, the pelletizing is accomplished by adding a binder, such as a heavy hydrocarbon, to the separated carbonaceous agglomerates, that is lyophobic to water and lyophilic to carbonaceous material to form a third mixture, and agitating the third mixture to dewater and pelletize the carbonaceous agglomerates.
Other details, objects and advantages of the invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the same proceeds.
US Referenced Citations (4)
Continuations (3)
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Date |
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115017 |
Jan 1980 |
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| Parent |
941055 |
Sep 1978 |
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| Parent |
540348 |
Jan 1975 |
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Continuation in Parts (1)
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608059 |
Aug 1975 |
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Patent Grant
4477353
