US 2769537 A
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United States Patent Ofiice $722111 PRODUCTION OF HIGH-GRADE PRODUCTS, ES-
PECIALLY FUELS, FROM RAW MATERIAL CON TAINING PIT COAL OR BROWN COAL Wilhelm Reerink, Essen-Bredeney, Walter Miischenborn, Essen, and Erich Niitzold, Essen-Hartkopf, Germany, assignors to Bergwerksverband Zur Verwertung Von Schutzrechten der Kohlentechnik G. m. b. H., Dortmund-Eving, Germany, a German company 7 No Drawing. Application November 6, 1951, Serial No. 255,132
13 Claims. (Cl. 20949) This invention relates to the production of high-grade products, especially fuels, from raw material containing pit coal or brown coal, which is present in fine-grained or extremely fine-grained form or is brought to the corresponding fineness.
The object of the invention is to provide a process by means of which, for example, intermediate and end products resulting from the normal method of dressing, such as sludges, dusts and the like, the finest fractions of crude coal, and any desired impure crude coals can be worked up by the Wet method, after suitable crushing and the like and with simultaneous water extraction, into pure products, the ash content of which can be adjusted as desired Within wide limits, which process can be carried out on a large scale by means of mechanical installations constructed in accordance with known principles.
Although numerous special processes for the dressing of fine and ultra-fine coal-containing material are known and have been put into practice, it is not usual in most cases to dress and utilize, for example, the sludges or any of the finest material, for example in coal-washing plant,
because the known processes are comparatively complicated and accordingly costly, exhibit very little selectivity and in addition are generally unsuitable for large-scale operation, while in addition even the pure products obtained are scarcely suitable for further use owing to their high water content. This also applies, for example, to the froth flotation method and to other known methods, in which the different wetting properties of the coal and waste components of the charged material with respect to oil and water are utilized to effect the separation.
The economic disadvantages arising from the aforesaid difliculties encountered in the working up of the finest material increase with the progressive mechanisation employed in the winning of coal, which leads to a further reduction in the particle size of the crude coal. Particular difliculties are caused in working up in the usual washing plant by reason of the high fine-grain content of the material, which cannot be completely separated off by prior dust extraction owing to the moisture content of the crude coal which results from the sprinkling effected at the working points in order to combat the dangers arising from dust. Moreover suificient facilities for utilizing dust of high ash content such as would be obetained by the pre-extraction of dust seldom exist.
These difliculties are overcome by the process according to the invention in which, as in known processes, the dilference in the wettability of the coal and waste components with respect to oil and water is utilized for the separation but not, as in the said processes, as for example in the froth flotation method, by causing the oil-wetted components to float to the top or, as in other known processes, by pressing the waste-containing particles together with the water out of a paste prepared from the starting material by the addition of oil and water-both of which steps are diflicult to carry out in large plants and are unsatisfactory in their efiectbut by a novel treatment ofa mass prepared by taking the crude material, pre-crushing it if necessary, and intimately mixing it with oil-containing substances, such as oil, tar, bituminous substances and the like, in kneading mechanisms, kneading pumps or the like.
In the said treatment the solid substances of such mixture are dispersed in a liquid, preferably water, after the oil treatment and thereby brought into a state such that the said dispersion can be separated, in a subsequent process step by mechanical means, preferably by centrifuging with simultaneous extraction of the water from the coal concentrate, into coal concentrate and waste particles suspended in water.
The dispersion of the mass consisting of coal, oil, waste and water, which is particularly important to the effectiveness of this process, is preferably effected in a heater mill or centrifugal mill in which the dispersion liquid (water) is added. The said dispersion may form a separate process step following the oil treatment in which case the consistency of the mass is so adjusted in the oil treatment, for example, that it is present in relatively dry crumbly form. Preferably, however, the dispersion is directly combined with the oil treatment, that is to say, it forms therewith a simultaneous indivisible process step in that the oil treatment is performed simultaneously with the dispersion in the presence of the quantity of water necessary for such dispersion. In this case the water emanates either from the starting material, for example if the latter material is present in the form of sludges, or in the case of dry or insufiiciently moist starting material it may be separately added, so that a material of pasty nature, or one which is already capable of flowing, is subjected to the simultaneous oil treatment and dispersion. The advantage of effecting the oil treatment and dispersion simultaneously, i. e. of the method last described, resides not only in the whole process being shortened and simplified but principally in the fact that the process is thereby rendered substantially independent of the water content of the starting materials and is thus directly applicable, for example, to a starting material which already has a sufliciently high water content if it is of sufi'iciently fine grain size, as in the case of sludges, tailings from flotation processes, intermediate products and the like.
The influence exerted by oils and reagents on the surfaces is particularly promoted if the masses to be treated, especially in cases where they have fairly high water contents, are forced by pressure, centrifugal action or suction through areas of narrow cross-section such as nozzles, slots and the like. This can be achieved in a favourable manner, for example, by means of high speed bafileplate mills having a delivery slot, or high-speed or highpressure pumps having attached nozzles or ven-turi tubes or the like. In this case it is advantageous to exert on the liquid a fairly high pressure which is adapted to the particular raw material and the oils and reagents which have been added. In the case of materials which are diflicult to treat it is preferable to repeat the treatment which can be done simply by connecting in series the machines employed for such treatment.
For the subsequent separation of the dispersion formed it is preferable to employ a sifting centrifuge or the like by means of which the waste-containing slime is expelled by centrifugal action while the oil-containing pure coal is obtained in a comparatively dry form. The waste sussuitable apparatus with the aid of water.
diameter of the perforations in the centrifugal sifting machines employed for this purpose may be substantially larger than the grain size of the mass of coal to be-worked up. This separating operation may be carried out in centrifugal machines of the most varied constructions in a single operation, either continuously or discontinuously. In addition to centrifugal sifting machines filters, separatorsand other suitable apparatus operating in a fundamen-tally similar manner and of a type known perse may be employed for this purpose. V
V The process results in a high-grade oil-containing; coal product 'suitable for use as fuel and for other purposes;
which has a low water content and which is obtained in loose form capable of being sprinkled'andcan therefore be efficiently rn'ixed with other materials, for'example fairly coarse finefcoal. The applicability of the process is 'substantially dependent upon the ash content of; the starting material, that is to say, the process can also be employed'to advantage for starting materials of high ash content, and in addition independently of the volatile components of the initial coal and of the degree of mina eralisation thereof; V
.It is particularly advantageousto employ for the productlon of'thestarting mass low-grade'oils, tars or, other bituminous materials Which'can otherwise only be utilized with difliculty, if at all, and insomecases materials'which are already present in the form of a water-oil emulsion, such as water-containing tar products, producer tars, oils obtained by boring and crude oils, that is to say'substances which generally contain other solid substances and V are otherwise practically valueless. stances which are not present in liquid form at normal temperature can be employed if a suitable temperature is maintained; a
vThe quantity of "oil to be employed depends upon the size of the surface of the coal fraction to be wetted; such quantity is preferably so great that the entire free surface of all the coal particles is wetted. If, for example, oil or the like containing impurities in the form of water and solid substances is employed as a wetting component, the quantity is related to the true oil fraction in the crude oil employed. Onthe other hand, however, the quantity of oil'must notbe too great since an excessive quantity gives ani'ntermediate or end product which is difiicult to handle' owing; to its unfavourable physical state.
In'additi'on it has been found that the wetting operation 7 and the separation of the wetted particles from the tailings' can be favourably influenced by varying the pI-I-value in the process step in question. In particular, the sedimentation of the wastecontained in the water is thereby accelerated. Accordingly it is preferable to ascertain by tests the optimum pH-values for each coal, which in turn depend upon the nature of the coal, the nature of V the admixtures, the oil component and the like. In many cases, it has been found preferable to adjust the slime to a pH-value at which the pyrites present in the material are readily separated olf. The course of the process can be favourably" influenced by the addition of regulating reag'entsin the treatment of the slime.
Where necessary the watercontent most favourable for eachistep of the process can be adjusted by the addition, and in some cases by the extraction, of water. Even a high water content of the initial material, as in the'case it may be'disadvantageous to the subsequent separating treatment in certain circumstances; In this case the desired water content of the dispersion to be subjected to Oil-containing subof dry coal, for example sifter dust of fine 'coal. The last described method is of particularadvantage, for-example,-
when applying the process to the working up of sludges emanating from the continuous operation of coal-washing plant in which case the fine coal washed in the normal washing process is added to the sludges which have been subjected to the oil and dispersion treatment before the separation step, and the extraction of water from the".
washed fine coal is thus combined with the separatioirof the sludges into coal and waste components with simul- 1 taneous extraction of the water.
Ifnormal hydro-extractors, as used forthe'extractionv of water from fine coal, are already available these may also be employed for the separating operation, whereby the further advantage is obtained that the finest particles *5 the fine coal are held fast by the oil-wetted, extremely fine coal particles, during the centrifuging operation and are prevented from being discharged through the. basket. A further advantage of this method of operation is that the oil-containing extremely fine coal particles from the worked-up sludge are simultaneously intimately mixed with the fine coal in the course of the centrifugal treatment and a subsequent separate mixing, for example Where it is employed as cokingcoal, is rendered rm? necessary. 7 v V V V 7 Generally, the new process cfiects a sufficient reduction of the ash content in one operation especially if the starting material is disintegrated to such an extent by the pre-crushir'ig that the intermixed components are separated from one another. If it is desired to reduce theash'content still'further this can be achieved by repeating one'or all of the operations described, if desired with an intermediate crushing 'of the material before the repeti: tion or an addition of further quantities of oil.
Owing to'the fact that the new process aifords the possibility of working up largequantities with comparatively simple apparatus the entire ultra-fine coal fraction previously separated from the crude fine coal for this purposemay be subjected thereto in a manner which is advantag'eous'for the normal washing operation of a coal washing'plant. e I
' The complete independence of the process according to the invention of the water content of the starting materials also simplifies any repetition which is necessary or" desired, either of the treatmentof the concentrates or of the Waste. In addition it permits very ad vantageous combinations of the new process with any other-Working-up processes which in themselves would not give end products of the required quality or which 7 would give 'such products only bycomplicated'meansa he separa ng t mentm y'be adj e y e. addition 5 Thus, for example, a crude coal present as ultra-fine coal,
or suitably crushed, can first-be subjected'to'preparation by flotation, treatment in a cyclone washer or by methods based on similar principles, for the purpose of separatingout the coarser waste components, whereafter the intermediate product is further worked up by the new process in the formin which it is'obtained.
One of; the most advantageous applications of the new process isthat in which it is employed to'produce coalproducts of particularly'low ash content, namely so-called precious coal or pure coal,'from which ultra-pure coat products having the required 'low ash content ca'n'be obtained practically without loss by a combination of'the' new process, with workingup processes known per se whichare applied to ultra-pure coal. v V The new .process is employed in combination with old processes in order to separate into-anoibcontaining coal.
concentrate of the normal 'comtne'rcial ash cohtentand pure wastethe tailings of high ash content which result. from the operation ofconcentrating'the ultra-pure coal, 7
the said separation being effected by subjecting the tail ings to the simultaneous oil and dispersion treatment V thereafter separating thedispersion'formed in a centrifugal V sifting machine or the like. Thus, a practically'complete,
recovery of the'coal components contained in the tailings in a m i w i t e can b u e s roses that is to .say, all coal losses are substantiallyavoided so that concentrates of any desired reduced .ash content can at the same time be economically skimmed off in the first stage of the combined process, i. e. .in the stage for concentrate thereafter separated in a centrifugal machine hadan ash content of 8% and a water content of 14%. The ash content of the waste tailings amountedto 79%.
the recovery of the purest coal, without regard to the IV coal losses in the intermediate products and without revgard to any optimum yield of coal of maximum purity. fe P of a 00211 grain of less t an If desired the concentrate from a preceding process for 1 W1th 235% 3511 y P P 3 ac .the dressing of pure or ultra-pure coal may be subjected r1110? h the p h Process 111 comblhatloh wll-h a P to the oil separation process similarly to the tailings with PllflfiCflhOIl y fl w-honthe object of further improving the quality of the ultra- The P g h Shows vthe PTOPOI'HOHS by Weight pure coal. of the various grain sizes and the ash content thereof In the following, a number of examples of the Various in the various process steps of the flotation and of the ,possib'ilitiesof applying the new process which have :been subsequent oil separation.
Flotation Oil Separation Charge Preconcentrate Waste I End product calc. Waste II Grain oil-free Weight, Ash, Weight, Ash, Weight, Ash, Weight, Ash, Weight, Ash; percent percent percent percent percent percent percent percent percent percent up to 1 mm 100 23.6 84. 7 l4. 5 15. 3 71 75.4 5. 8 9. 3 80 described above will be given but the possible ways of 30 Consumption of oil in the flotation, 12. k-g./t. Oil
applying the process are naturally by no means limited thereto:
A. FUNDAMENTAL PROCESS A gas coal of such grain that about 90% thereof passes through a. screen having 10,000 meshes per sq. cm., and leaving .a water and 22% ash content, was fed with 8% (calculated on dry coal substance) of a mineral oil residue containing water and mineral constituents .to a continuously operating kneading pump after brief premixing in a paddle worm. The mixed material thus obtained was fed together with water to a cross beater mill for the purpose of dispersion and the dispersion thus obtained was separated in va centrifugal sifting machine into ash-free coal fraction and waste-water fraction. The coal fraction had an ash content of 4% (water free) and a water content of 14%. The ash content of the waste simultaneously delivered amounted to 80%. The diameter of the perforations of the sifting machine employed amounted to 0.2 mm.
A fat coal of such grain that 50% thereof passes through a screen having 10,000 meshes per sq. cm., and having a 25% water and ash content, was briefly pre-mixed in a mixer with 18% (calculated on the dry coal substance) of tar obtained by the distillation of brown coal and then passed through a kneading pump. The mixed material was then fed with water to a disintegrator and finally separated in a centrifugal machine into ash-free coal substance and waste-water fraction. The coal concentrate had a water content of 12% and an ash content of 7% (Water-free). The waste contained 75% ash. The size of the sifting slots amounted in this case to 0.25 x 4.0 mm.
Working up of a fat coal sludge of high water content with 50% grain sizes below 0.6 mm., 19% ash and 400 g. of solid substances per litre.
The sludge was intensively mixed after the addition of reagents and about 4% of oil, calculated on the dry solid substance, the influence of oil and reagents on the particles and the ultra-fine division of the solid substances in the slime being simultaneously effected. The oil-coal added in the oil separation, 50.0 kg./ t.
Gas coal sludges containing 23% ash were subjected to the oil separation process. The sludges pre-treated with oils and reagents with simultaneous dispersion in a baflle plate mill comprising a centrifuging wheel and a slot delivery were separated on a cellular suction filter with two washings and freed from water. The filter cake had a water content of 16.7% and an ash content of 8.6%. The Waste tailings had an ash content of 84%.- A Perlon filter fabric having'a mesh width of 0.25 mm. was employed.
1. A process for removing the ash content and -dewatering coal-containing raw material which comprises intimately mixingsaid coal-containing raw material in finely divided form with an oil-containing substance to wet the individual coal particles with an oil film which replaces the water film previously thereon, while simultaneously dispersing the mixture in water to form a flowable dispersion by forcing the water-containing mixture through openings of narrow cross section, and thereafter mechanically separating the resulting dispersion into coal concentrate and waste water containing the ash in finely divided form.
2. The process of claim 1 in which the dispersion is maintained under superatmospheric pressure.
3. The process of claim 1 in which the dispersion is directed through screen openings of substantially larger size than the grain size of the bulk of the oil-wetted coal particles, the coal particles being retained in dewatered 7 state by said openings as a result of the oil film coating them.
4. The process of claim 1 in which the separation of the dispersion and the dewatering 0f the concentrate is efiected by means of a screen centrifuge.
5. The process of claim 1 wherein the oil-containing substance is not liquid at ordinary temperatures but wherein the process is carried out at a temperature above the melting point of said non-liquid, oil-containing substance.
6. The process of claim 1 wherein the pH of the dispersion is adjusted to effect the ultimate separation of any pyrites contained therein.
7. The process of claim 1 wherein normally washed fine coal is added to the dispersion and the resulting mixture subjected to a dewatering process employing fine coaljscreen centrifuges.
- 8.; A process j for I removing I theglash content dej watering "coalcontaining raw "material which comprises treating the coal with a heavy liquid to produce purified fine-grainfloating coal and Settled waste, separating the wasteirom the fine-grain coal, intimately said sion by forcing -the.'water-containing mixture through openings of narrowcross section, and. thereafter'mechanically separating the resulting dispersion into coal concentrate and waste watercontaining the ash in finely divided form.
9. The process of claim S Wherein the heavy liquid is part of the. Waste Water from the dispersion separation.
10. The process of claim 8 wherein only the fine coal from the floating material is subjected to the simultaneous oil treatment and water dispersion and subsequent separation. 7 '11. A process for removing the ash content and dewatering coal-containing raw material which comprises intimately mixing said coal-containing raw material in finely divided form, having a grain size not in excess of 1 mm.,' with an oil-containing substance to wet the individual coal particles with an' oil film which replaces the water film previously thereon, and simultaneously dispersing the mixture in water to form ra fiowable dispersion by forcing the water-containing, mixture through openings of narrow cross-section, and thereafter mechanically separating the dispersion into oil-containing coal concentrate and wastewater containing the ash in finely divided form. I
' 121A process for removing the ash'contentand dewatering coal-containing raw material which comprises intimately mixing said coal-containing'raw material in finely divided form, having agrain size not' in excess of '1 mm., with an oil-containing substance to wet theindividual coal particles with an oil film which replaces the water film previously thereon, and simultaneously dispersing the mixture in water to form a flowable dispersion by forcing the water-containing mixture under pressure through openings of narrow cross-section, and thereafter mechanically separating that dispersion into oil-containing coal concentrate and waste Water containing the ash in finely divided form,-
8 said separation being efiected by passing the dispersion through ajscreencentrifugehaving screen openings of substantially larger size than the grain size of the bulkof the oil-wetted coalparticles, the coal particles being retained in dewatered state bysaidopenings as aresult of the oil film thereon. n
13. A process for removing the' ash content and dewatering a fat coal sludge having grain sizes below 0.6 mm., 19% ash and 400 g./liter of solid substances, which comprises intimately mixing said sludge with about 4% oil, based on the dry solid substances, to wet the individual coal particles with an oil film which replaces the water film previously thereon, andsimultaneously dispersing the mixture in water to form a flowable dispersion by forcing the water-containing mixture under pressure through openings of narrow cross-section, and thereafter mechanically separating the dispersion into oil-containing coal concentrate and waste water containing the ash in finely divided form, said separation being eflfected'by passing the dispersion, through a screen centrifuge having screen openings of substantially larger size than the grain size of the bulk of the oil-wetted coal particles, the coal particles being retained in dewatered state by said openings as a result of the oil film thereon.
1 References Cited in the, file of this patent UNITED STATES, PATENTS 422,907 1 Bowing; Mar. 11, 1890 676,679 Elmore'.. June 18, 1901 736,381 Glogner Aug. 18, 1903 762,774 Van Meter et al June 14,1904 763,859 Darling June 28, 1904 807,505 Schwartz' Dec. 19, 1905 1,367,223 Appelgrist et'al Feb. 1, 1921 1,420,163 Trent June 20, 1922 1,420,164 'Trent Iune'20;1922
1,421,862 l Trent July'4, 19 22 1,512,427 Trent Oct, 21, 1924 1,538,270 Collier May 19, 1925 1,667,277 Wilkinson Apr; 24, 1928 1,838,884 Trent Dec. 29, 1931, 1,867,783
Trent i 19,1932
OTHER REFERENCES Taggart, Handbook'of Ore Dressing (c), 1927, by John V Wiley & Sons, Inc., page 783.