US2176129A - Coal treatment - Google Patents

Description

Patented Got. 17, 1939 UNITED STATES 2,176,129 coAL TREATMENT Harvey 13.. Fife, Pittsburgh, Pa.

No Drawing. Application October '26, 1937. Serial No. 171,098

6 Claims.

In the course of experience it has become a recognized fact that carbonaceous fuels of the various types designated broadly by the term coal, are greatly improved by protective treat- 6 ment conducted at some stage between the mining and combustion of the coal. There are various aspects to the protective treatment of coal, sounding in economy, in safetyjin cleanliness, and in uniformity of combustion qualities. From 10 its nature coal is subject to degradation both by weathering and by mechanical breakage, the latter being the factor preponderantly responsible for the degradation 'of coal. Such breakage, when it occurs at the mine, gives increased difficulty in sizing, and detracts from the'value of the coal, which, itmay be assumed, is most valuable when it is in a condition of approximately fly dust. In the tipple the coal is graded as to size, as by screening, and a certain proportion of the slate forming the major inorganic contamination is removed. The operation of screening itself causes degradation, since the coal particles as received in the tipple in some proportion fracture in the screens to form smaller sizes, and by fracture and abrasion produce an increased proportion of fines and of ily'dust. After coal has 40 been screened, it is not only in most instances exposed to weathering, but is inevitably exposed to the degradation-producing efiects of transpontation and handling. For example, if domestic coal be loaded in freight cars and conveyed t'b 'a central depot, it is subject to breakage while'b'elng loaded upon and unloaded from the cars, ahH -t'o rubbing and jarring. during transit. A 'si possibility of degradation occurs in a tru' veyance from a central depot to the po ultimate use, and in most instances the ther possibility of degradation in the r the coal to the furnace, or into a stolf i'? be understood that throughout theefi intervening between its mining and it dimensions and less, and a certain proportion of PATENT OFFICE tion the coal is subject to degi; a tion of its exposed surface. 3 It may be assumed that all and to render useful and de Y which would otherwise be aste) possess undesirable feat' lary objects in the tre coal, and to sqm coal. Variou ,gra oil have bee coal by the application of a wax blend, such as petrolatum, cannot be considered to be practical merely in the fact that these materials are applied indiscriminatelyto coal of various types at some stage in the history of the coal.

The conditions under which satisfactory treatment of coal may be most readily had are those in which a coal of good grade, clean and approximately dust-free, is sized before treatment, and in this connection I mean by coal of good grade, a coal which is dense, relatively non-friable, and which does not possess marked cleavage planes creating a tendency readily to fracture. Upon coal of that sort and under those conditions a treatment with petroleum oil even if of relatively low viscosity is advantageous, and the higher viscosity cuts of petroleum applied with heat in the form of a spray are in approximate proportion to increasing viscosity increasingly advantageous. It is also possible with reasonable satisfaction to apply petrolatum to clean, sized and relatively dust-free coal, by spraying, under simple air pressure, petrolatum rendered sprayable by being heated to above its melting point. When coal is clean and sized, petrolatum may also be applied very satisfactorily by dipping the coal in a warm water suspension of the petrolatum, or by a low pressure spraying of such water suspension upon the coal.

Coke may be considered as a clean and sized coal, and as such may satisfactorily be treated by spraying it with petroleum oil or a wax-oil blend. As it may, however, be treated with advantage by the specialized method herein disclosed, I intend in the appended claims to include it by the generic term coal.

It may be generally stated that in comparison with a petroleum oil as such, irrespective of the viscosity of the oil, a petrolatum in which there is any substantial content of wax is superior to a simple oil. Petrolatum does not crawl upon the surface of the coal, as does oil, and is less subject than oil to mechanical removal; thereby continuing for more extended periods of time and under more severe conditions of handling so to lubricate the coal as to minimize breakage, and also the more efficiently and for a longer period to minimize dust formation in a body of coal. Petrolatum by possessing a lesser tendency to crawl than does oil posssesses a further advantage over oil, in that it does not in like manner collect in the receptacles or bins in which the coal is transported or stored.

Whether a simple oil or a plasticized wax, such as petrolatum, be used for the treatment of coal, departure from the ideal conditions above described increases the difliculty of satisfactory treatment. Thus in treating run-of-the-mine coal it is necessary in sprayingthe coal with a treating material that the spray be so finely atomized as to penetrate the mass of coal and to find lodgment upon all surfaces of each coal particle. In order to obtain optimum results it is necessary that dust and fines present in the bodyof coal, and which when present in any proportion by weight constitute a very large proportion of the surface area of the coal, should not take to themselves an undue proportion of a coating material during the treating operation. This is important from the viewpoint of economy, in order that the conduct of the process may be efficient, and in order that the fines, such as coal particles from inch down, may not carry such quantity of the oil or wax that difficulty is experienced in pulverizing them for use in blowers and the like.

It should be further understood that in dealing with a mist of either oil or Wax so finely atomized as to be applied uniformly to the surfaces of the coal particles of various sizes, there is a fire and explosion hazard which must in practice be. given careful consideration. It may also be assumed that in order to cover the coal particles there must be either an instantaneous flow of the material on the surface of the coal particles, or the mist of oil or petrolatum (and this is particularly true in the case of petrolatum) must be so fine that the coal particles are instantly covered by impingement with the mist. It may be noted that in treating coal which has a substantial content of fly dust there is an electrical phenomenon which must be taken into consideration from the viewpoint of safety. Coal dust particles readily take a static electrical charge and as charged are, when present in quantity, frequently capable of delivering a spark causing a dust explosion in which the mist of oil or wax, as well as the dust particles themselves is involved. If high vis cosity oil or petrolatum are applied by air pressure spraying with the application of heat suffi cient to render them adequately sprayable, the mist thus produced has itself a static charge and is incapable of individually discharging the coal dust particles within the spray zone. The same condition is encountered in the simple air spraying of low viscosity oil. Coal dust being present in variable quantity, it is difficult to form an atomized mist of petroleum oil or petrolatum rich enough for satisfactory treatment without incurring serious explosion risks.

I have discovered that the association of steam in the spraying zone with a finely atomized mist of petroleum oil, or the petroleum-derived petrolatum which has been above defined, greatly reduces explosion and fire hazards. I have further discovered that if such steam pass through the spraying zone at low velocity, and at a corresponding temperature, it is a useful adjunct in the actual deposition of the oily petroleum-derived treating material upon the coal, and does not, like high velocity steam used for atomizing, detract from the effects desired from deposition of the treating material on the coal. That is, it does not serve to carry coal dust and the atomized treating mist out of contact with the coal. In reducing explosion and fire hazards a steam dilution of the mist is more effective than an air dilution, both because it does not itself provide an explosive mixture with either the hydrocarbon mist or the coal dust, and also because it serves individually to discharge the static electrical charge carried by the particles of the coal dust.

In accordance with my preferred procedure in treating run-of-the-mine coal at the tipple I pass the coal with agitation, as in a falling stream, through a spraying zone in which it is acted upon by a mist of finely atomized petroleum treating material commingled with low velocity steam. Atomization is in the case of high viscosity petroleum oil and petrolatum effected by a pump pressure which is desirably high, for example, a pump pressure of the order of 400 pounds per square inch and upward at the spraying nozzle, the spraying of the high viscosity oil or petrolatum being facilitated by superatmospheric temperature, which in the case of petrolatum is above the pour-point of petrolatum. In the case of high viscosity oil, assuming that high pressure is used, a temperature which reduces the viscosity of the oil to from 600 Saybolt seconds at F. to 800 Saybolt seconds at 100 F. is adequate.

Desirably I utilize a steam coil to raise the temperature of the petroleum treating material in passage to the spraying nozzle.

In spraying low viscosity oil in this manner, in association with low velocity steam, the oil need not under all conditions be preheated for spraying and application to the coal. For example, I have found it unnecessary to preheat oil of viscosity up to about 600 to 800 Saybolt seconds at 100 F. if the atomizing pressure be of the order of about 300 pounds per square inch or rnore. For lower viscosity oils the pressure may be proportionally decreased without recourse to preheating, and if high viscosity oils are preheated to viscosities below 600 to 800 Saybolt seconds at 100 F., the spraying pressure may be correspondingly lower than 400 pounds per square inch. At that pressure lean petrolatum blends having pour-points at unelevated temperature may be sprayed without preheating.

Whether the spraying be efiected by preheating or high pressure, or both, the effect of the low velocity steam in the finely atomized mist is identical Since the steam which is added to the petroleum mist is not depended upon to atomize the oil or petrolatum, it may be released at low velocity, and I have with satisfaction utilized steam within a boiler pressure range of from 10 pounds per square inch to 250 pounds per square inch. If the steam is expanded at'the spraying nozzle, as for example to surround the atomized mist of hydrocarbon material in a cone it is desirably an initially low pressure steam. If,.- however, the steam to be expanded into the spraying zone at some point substantially removed from the spraying nozzle a smaller quantity of steam at higher pressure is, when expanded, substantially equivalent in diluting the mist with low velocity steam. 1

More specifically to describe my preferred .procedure, I have found it desirable to provide one pound of steam for each pound of the hydrocarbon material. This ratio, however, is subject tovariation within relatively wide limits in accordance with the volume of the spraying zone and other factors which may influence the effect of the steam. The spraying zone is .established by the relative position of the spraying nozzle, or nozzles, and the instrumentality which delivers the coal, and is also defined by instrumentalities which in practical effect confine the treating mist to a limited volume. For example, I have found it desirable to utilize a spray hood surrounding the spraying nozzle, or nozzles, and the end, or a limited region, of the apparatus which conveys the coal.

When the coal is passed through the spraying zone in a falling stream, as is most desirable, I prefer to position the spraying nozzles as close to the stream as is possible, and have found that I I may under most circumstances, and in treating run-of-the-mine coal position nozzles within a foot of the under side of the coal stream and may position nozzles within three feet of the upper side of the coal stream. The spraying zone isthus permitting them to coagulate. By giving up its heat of condensation in the spraying zone, the steam also contributes to the uniform thin distribution of the hydrocarbon material over the surfaces of the coal particles.

and thereby to remove from the tipple any such proportion .of the spraying mist and coaldust as may tend to escape from the spraying zone.

In considering the advantages of the treating process above described, it should be appreciated that run-of-the-mine coal frequently has a proportion of its surface equal to about to of the whole represented by coal particles which are less than inch in dimension. Such fraction would represent 10% to 30% the total weight of the coal. portion of the fines be formed into larger particles without gathering a larger proportion of the treating material than is commensurate with its surface area. The portion below '200 mesh in particle size becomes particles of non-flying character without so agglomerating the particles that immediate normal screening is inhibited. Also by preventing undue accumulation of treating material by them, the more substantial fines are in better condition for subsequent pulverization, or immediate screening. An additional advantage of the method is that the condition of the mist leads to the coating of the slate content of the run-of-the-mine coal, thus protecting it against breakage in screening and subsequent degradation into a particle size so small that it would tend to segregate in the lower region of a stored mass of the coal.

I have found that in preparation for screening and mechanical cleaning, if that be employed, a very thin deposit of petrolatum is sumcient to minimize degradation of the coal by fracture or abrasion during these operations. For example, I have obtained excellent results in preventing degradation at the tipple by applying to run-ofthe-mine coal from 2.3 pounds per ton to 2.5 pounds per ton of petrolatum, consisting of 70% by Weight wax and 30% by weight associated oil, in accordance with my preferred procedure as outlined above. The surface area of a ton of run-of-the-mine coal is a variable quantity, because of varying breakage of the coal in mining. It is well therefore to explain that I have obtained satisfactory results by applying petrolatum (70% wax content) to coal in a quantity of from .001'to .004 pound to each approximate square yard of coal surface. The quantity actually used within this quantity range is roughly proportioned inversely to the ability of the coal to withstand blows and abrasion.

While I have found wax-free petroleum oil to be less effective in protecting run-of-the-mine coal against degradation at the tipple than is petrolatum, advantage in minimizing fire and explosion hazards, and in degree in lessening waste of treating material, is obtained by a treatment similarly conducted with oil.

When conducting my process with petroleum oil, instead of petrolatum, as the oily petroleum treating material, like quantities by weight of oil per .unit area of coal surface are desirably applied. This is so, although the oil is less efiective' than an equal quantity of petrolatum in protect- It is important that the fly dust ing the coal against breakage and abrasion, for the reason that the application of an undue quantity of oil to the coal seriously interferes with the normal operation of screening.

For certain uses, it is desirable to apply an added coating (preferably petrolatum) to the coal after screenings Such final treatment is of particular utility in the case of stoker coal and other domestic sizes, which have had their dust content removed by screening. Although in such treatment the dust problem is negligible, the reduction in fire and explosion hazard renders the addition of low velocity steam to an otherwise atomized treating mist of great practical importance. Since this final treatment may be conducted outside the tippleor other enclosure, the use of the low velocity steam may be associated with an air or steam atomization of the oily petroleum treating material to counteract the fire and explosion hazards of such spraying, and to decrease the waste of finely atomized mist attendant upon air or steam spraying.

It may be assumed that in the pretreatment of coal in the tipple, petroleum oil may with fair satisfaction be used upon coal of the sorts which are of themselves particularly resistant to breakage and abrasion. In a final treatment of coal petrolatum has universal advantage over petroleum oil, due to the increased life of a petrolatum film as compared with an oil film on coal, and in the superior cleanliness of coal treated with petrolatum. I do not, however, exclude from a final treatment conducted in accordance with my method, petroleum oil as the oily petroleum treating material used.

In this final, or secondary, treatment I have found it desirable to increase the quantity oi. applied coating material to from .006 to .(ll i pound per square yard of coal surface, and if the noncrawling petrolatum be employed, I have found it desirable so to place the spray nozzles that a greater proportional quantity of the film is deposited on the larger coal particles. .This permits collection of dust particles on coal particles of those sizes from which dust particles are least likely to be-removed by wiping. Since such relatively thick film is of a non-crawling nature it may continue to function in dust collection during long continued storage and handling. The above selective application of petrolatum I efl'ect by so distributing the number of spray nozzles that a preponderant proportion of the treating material reaches the upper side of a coal stream as it changes its direction to fall by gravity from a boom, or the like apparatus.

It'is to be understood that when-I speak of petroleum oil I mean either paraffln base, mixed base, or asphalt base petroleum oil; and although asphalt base petroleum does not serve as a source of petrolatum, it may be used in blending with wax artificially to produce a wax-oil blend responding to my definition of petrolatum.

I claim as my invention:

1. The herein described method of protectively treating coal with oilypetroleum material which comprises atomizing an oily petroleum material into a fine mist by subjecting it to extraneous mechanical pressure at a spray nozzle, and while passing the coal to be treated through a treating zone of the said finely atomized mist independently adding steam at low velocity and lowtemperature to the said finely atomized mist, to supply to the coal independently of the said mist heat for flowing the oily petroleum material of the mist over the coal and to apply moisture at the surface of the coal.

2. The herein described method of protectively treating coal with petrolatum which comprises atomizing petrolatum intoa fine mist by subjecting it to extraneous mechanical pressure at a spray nozzle, and while passing the coal to be treated through a treating zone of the said finely atomized mist independently adding steam at low velocity and low temperature to the said finely atomized mist to supply to the coal independently of the said mist heat for flowing the petrolatum of the mist over the coal and to apply moisture at the surface of the coal.

3. The herein described method of protectively treating coal with oily petroleum material which comprises forming and projecting a finely atomized mist of an oily petroleum material at a spray nozzle by subjecting it to extraneous mechanical pressure, and while passing the coal to be treated through the said mist of oily petroleum material confining and diluting the said finely atomized mist by independently and simultaneously projecting toward the coal a mist of low velocity low temperature steam serving also to supply to the coal heat for flowing the oily petroleum material over the coal and serving to apply moisture at the surface of the coal.

4. The herein described method of protectively treating coal with petrolatum which comprises forming and projecting a finely atomized mist of petrolatum at a spray nozzle by subjecting it to extraneous mechanical pressure, and while passing the coal to be treated through the said mist of petrolatum confining and diluting the said finely atomized mist by independently and simultaneously projecting toward the coal a mist of low velocity low temperature steam serving also to supply to the coal heat for flowing the petrolatum over the coal and serving to apply moisture at the surface of the coal.

5. The herein described method of protectively treating screened coal with oily petroleum material which comprises atomizing oily petroleum material into a fine mist in a spray nozzle, and

,directing the said finely atomized mist of oily petroleum treating material upon coal which has previously been screened while independently and simultaneously projecting upon the said screened coal low velocity low temperature steam to supply to the coal independently of the said mist of oily petroleum material heat for flowing the oily petroleum material over the coal and to apply moisture at the surface of the coal.

6. The herein described method of protectively treating screened coal with petrolatum which comprises atomizing petrolatum into a fine mist in a spray nozzle, and directing, the said finely atomized mist of petrolatum upon coal which has previously been screened while independently and simultaneously projecting upon the said screened coal low velocity low temperature steam to supply to the coal independently of the said petrolatum mist heat for flowing the petrolatum over the coal and to apply moisture at the surface of the coal.

HARVEY R. FIFE.