Pressure-reducing spray nozzle and use thereof in a froth flotation method

#The present invention relates generally to an apparatus and method for flotation separation of mineral particles including coal and similar materials, and more particularly pertains to an improved apparatus and method for beneficiating coal by flotation separation of a froth generated by a pressure-reducing spray nozzle such that ground coal particles may be separated from impurities associated therewith such as ash and sulfur.

#Coal is an extremely valuable natural resource in the United States because of its relatively abundant supplies. It has been estimated that the United States has more energy available in the form of coal than in the combined natural resources of petroleum, natural gas, oil shale, and tar sands. Recent energy shortages, together with the availability of abundant coal reserves and the continuing uncertainties regarding the availability of crude oil, have made it imperative that improved methods be developed for converting coal into a more useful energy source.

#Many known prior art processes for froth flotation separation of a slurry of particulate matter are based on constructions wherein air is introduced into the liquid slurry of particulate matter, as through a porous cell bottom or a hollow impeller shaft, thereby producing a surface froth. These prior art methods are relatively inefficient approaches, especially when large amounts of particular matter are being processed. Generally, these techniques are inefficient in providing sufficient contact between the particulate matter and the frothing air. As a result, they require relatively large amounts of energy to generate the froth. In addition, froth flotation techniques which permit bubbles to rise in the slurry can tend to trap and carry impurities such as ash in the froth slurry, and accordingly the resultant beneficiated particulate product frequently has more impurities therein than desired.

#The foregoing spray apparatus and froth flotation method may be more readily understood by reference to the drawings in which:

#FIG. 1 is a schematic view of a froth flotation system in accordance with the teachings of the present invention; and,

#FIG. 2 is a schematic of a double deflecting spray apparatus in accordance with the teachings of the present invention.

#The double deflecting spray apparatus and method of the present invention are adapted to the separation of a wide variety of solid-fluid streams by the creation of a solids-containing froth phase, and are suitable for the separation of many types of particulate matter. However, the present invention is described herein with specific application to a coal beneficiating operation.

#It is preferred to employ a coal-aqueous slurry having a coal to water ratio of from about 1:25 to about 1:2 and preferably from about 1:20 to about 1:5 parts by weight, especially one in which the coal component has been previously beneficiated. Any of the known and conventional beneficiation procedures and apparatus are suitable, e.g., the beneficiation systems described in U.S. Pat. Nos. 4,304,573; 4,332,593; 4,347,126; 4,347,127; 4,406,664; and 4,412,843, the disclosures of which are incorporated by reference herein. In particular, in accordance with the beneficiation system described in aforesaid U.S. Pat. No. 4,412,843, coal or other carbonaceous material, generally of a particle size of from about -10 to less than about 500 mesh, preferably with about 80% of the particles being of -200 mesh in size (Taylor Standard Screen Size), is admixed in an aqueous medium with a surface treating mixture comprising a polymerizable monomer, a polymerization catalyst and a liquid organic carrier thereby rendering the coal hydrophobic and oleophilic. The thus-beneficiated hydrophobic and oleophilic coal particles float to the surface of the liquid mass while the ash, still remaining hydrophilic, tends to settle and is removed to the water phase. The beneficiated coal particles in the form of a froth are recovered, e.g., by a skimming screen, and are thereafter optionally subjected to at least one further wash step.

#The beneficiation process of U.S. Pat. No. 4,412,843 can employ any polymerizable monomer, preferably one which is ethylenically unsaturated such as ethylene, propylene, butylene, tetrapropylene, isoprene, butadiene, pentadiene, dicyclopentadiene, octadiene, olefinic petroleum fractions, styrene, vinyltoluene, vinylchloride, acrylonitride, methacylonitrile, acrylamide, methacrylamide, N-methylolacrylamide, acrolein, maleic acid, maleic anhydride, fumaric acid, abietic acid, and the like. Unsaturated carboxylic acids constitute an especially preferred class of polymerizable monomers and include fatty acids such as oleic acid, linoleic acid, linolenic acid, ricinoleic acid, mono-, di- and tri-glycerides and other esters of unsaturated fatty acids, acrylic acid, methacrylic acid, methylacrylate, ethylacrylate, ethylhexylacrylate, tertiarybutylacrylate, oleylacrylate, methylmethacrylate, oleylmethacrylate, stearylacrylate, stearylmethacrylate, laurylmethacrylate vinylacetate, vinylstearate, vinylmyristate, vinyllaurate, unsaturated vegetable seed oil, soybean oil, rosin acids, dehydrated castor oil, linseed oil, olive oil, peanut oil, tall oil, corn oil, and the like, with corn oil providing especially good results. The amount of polymerizable monomer will vary depending upon the degree of surface treatment desired. In general, however, monomer amounts of from about 0.005 to about 0.1% by weight of the dry coal are used.