US1912697A - Method of treating coal - Google Patents

Description

Patented June 6, 1933 UNITED STATES PATENT OFFICE HARVEY R. FIFE, 'OF PITTSBURGH, PENNSYLVANIA METHOD OF TREATING GOAL No Drawing.

combustion, particularly if there is present with the coal a substantial quantity of dust therefrom. As is well known, this dust will also form an explosive mixture with the oxygen of the atmosphere. A previously known method of'laying coal dust is to spray the coal in bulk with a solution of an inorganic substance, such as calcium chloride, and thereby form a coating over the lump coal and the dust therefrom.

The method of my present invention is particularly valuable for use with lump coal.

I have discovered that an effective and economical method of protecting the coal from deterioration and oxidation, is to cover the surface of the coal with a. thin adherent coating or tegument of a combustible and viscous substance. As such coating substance I prefer waxes and low melting tars or asphalts. It is necessary that the coating or tegument be viscousin order that it may seal the coal within a suitable envelope, in order that it may solidify on the surface of the coal, and in order that the ignition temperature of the coal may not be materially affected. For these reasons the coating material should be applied in a highly fluid condition, its viscosity being lower than the normal viscosity of the coating substance at room temperature. This fluidity may be obtained by means of a suitably applied temperature sufficiently high to secure fluidity of the coating material.

One mode of, application, which I have employedsuccessfully, is to dip the coal by suitable means, such as' a belt conveyor in a bath of melted paratlin wax. The coal'is introduccd at room temperatures, so that the wax tends to congeal on the individual lumps and particles of coal.

The coal so coated is then removed. from the bath and is subjected to a flowing step,

Application filed June 25, 1930. Serial Noi 463,838.

which consists in subjecting the coal to a higher temperature, materially above the melting point of the wax. The step causes the wax to so flow over the entire surface of each lump or particle of coal that upon congelation it provides a thin, sealed, coating or tegument of semi-solid material on each lump or particle.

When the coal is dipped in melted wax, the

flowing step is essential in order that the coating on the coal may be thin and continuous to form the desired sea-l.

Another mode of applying the coating, by means of a heated bath, consists in utilizmg parafiin wax, orlother suitable coating material, in a suspension, or mechanical mixture, with heated water. Assuming that paraffin wax is used, a bath may be prepared by raising the water to a temperature mate rially above the melting point of the particular wax which is to be applied to the coal. The melting point of the wax used will vary considerably with different runs inasmuch as it is desirable, for reasons of economy, to use unrefined wax obtained as a residue from the distillation of paraflin base petroleum; but in any case the temperature of the bath, as noted above, should be materially higher than the melting point of the wax, in order that it may flow readily and adhere to the coal in semi-solid state, as a uniform coating, in order to seal the lumps or particles of coal. I

With suspension, or mechanical mixture, of melted wax and water, the coal is dipped in the bath and may be rapidly removed therefrom. As a typical example a bath is prepared by adding 1 to 5% by weight of paraffin wax to the water and raising the temperature of the water by the application of heat in any suitable manner. I have found that this temperature should be at least 5 degrees centigrade above ,the melting point of the coating material, and may desirably in some instances be as high as 50 degrees Centigrade above the melting point. In general I have, found satisfactory a temperature .of 20 degrees centigradc higher than the melting point of the wax, or other coating material, used. The coal is then passed through the its concentration with respect to the wax suspended in the water thereof, and the duration of the dipping step. The coal as.

19 passed through the bath is substantially at room temperature and the deposition of the wax is, therefore, rapid if. the temperature of the bath is sufficiently high. Avoidance of a coating which may be so thick as tobe wasteful or so thick that it will remain objectionahly sticky or tacky upon solidification, is avoided both by an adequately high bath temperature, hy the inclusion of a relatively small quantity of wax in the bath with respect to the suspending liquid, and by an adequate period of immersion.

I have obtained good results by preparing a bath containing water and paraffin wax, the wax being added in a proportion of three per cent. by weight and raising the temperature of the bath to 65 degrees centigrade. I then dipped the coal in the bath while subjecting the bath to rapid mechanical agitation and removed it therefrom after an immersion of a few seconds. Lumps of coal, having a relatively great surface area with respect to their weight were covered with a sealed coating of wax the weight of which was .7 or less the weight of the coal.

Instead of dipping the coal in a bath, a suspension may be prepared by agitating the wax with water while heating the mixture to form the suspension, and spraying the mixture of water and wax on the coal which is to be coated. In so applying the coating Wax to the coal, it is necessary to exercise care to assure the high temperature of the mechanical mixture of wax and water at the instant of its physical contact with the coal.

45 Various alternative substances may be used in place of the paraffin wax. For example, I have used neutral pitch and neutral a-sphalts, which latter may be either neutral asphalts of natural occurrence or neutral a'sphalts resulting as a still residue.

In utilizing any of these substances I have found it important that they be so produced or treated that they are in neutral, rather than acid, condition. This is for the reason that the coating material should form a mechani al mixture with the water, rather than an emulsion therewith. In using an emulsion there is a tendency for the material deposited therefrom to gather in lumps or globules on the surface of the coal, rather than'to spread thereover in the desired thin and adherent coating-to form an individual seal for each lump or particle of coal.

It should be understood that in using pitch, asphalt, rather than paraffin wax, as a coating material, the same general mode of application may be employed and the same factors are of importance. It is important that the tar or asphalt be mixed with the carrying liquid in a relatively small proportion; that the temperature of the liquid be materially higher than the melting point of the tar or asphalt; and, if the coal be dipped, that the period of immersion be of sufficient duration 'and the secondary flowing step be at a high temperature, to secure an adequate flowing of the tar or asphalt to produce the desired thin, sealed, coating.

It may be noted that the application of the coating material by a mechanical mixture of the coating material with a carrying liquid requires no flowing step, the flowing effect being obtained in the bath itself or by the dispersion of a spray applied at a high temperature.

It should be understood that while water has been mentioned, other carrying liquids may be employed if so desired. Insofar as this manner of conducting the method is concerned, the requisite qualities of the carrying liquid are that it have a relatively high boiling point, so that the desired high temperature of the suspension may be attained, and that it is a liquid in which the coating material is insoluble or sparingly soluble. It should be further understood that a mixed coating material, as for example a mixture of paraffin wax and asphalt, may be employed if the temperature of the suspension is materially higher than the melting point of the mixture.

It may be generally noted that my method provides the coal with a coating so thin that it does not increase the fire hazard by applied flame while decreasing the fire hazard from spontaneous combustion. The coating is also so thin that there is no marked tendency toward agglomeration of the lumps or particles of the coal in handling and shipping, such as would be the case if a relatively thick coating of objectionably sticky material were applied to the individual lumps or particles.

My method thus differs widely from previous methods in which the object has been to cause the agglomeration of fine particles of coal, or other combustible solid, with a viscous substance which may be added in a relatively great proportionate quantity, to form a mixed mass with the solid fuel particles.

What I claim is:

1. The method of protecting coal from dusting and oxidation which comprises subparticles in a thin-film, and permitting the wax to congeal during cooling to normal room temperature to form a thin sealed coating of semisolid material on each individual and unag lomerated particle.

2. The method of protecting coal from dusting and oxidation which comprises sub- -jecting the coal to a bath containing paraffin wax in liquid suspension, the temperature of the bath being materially higher than the melting point of the wax to flow the wax over the entire surface of the individual coal particles in a thin film, and permitting the wax to congeal during cooling to normal room temperature to form a thin sealed coat- I ing on each individual and unagglomerated particle. I

3. The method of protecting coal from dusting and oxidation which comprises subjecting the coal to a bath containing paraffin wax in liquid suspension, the wax being present in a proportion of from one per cent. to five per cent. the weight of the liquid, raising the temperature of the bath to a point materially higher than the melting point of the wax to flow the wax over the entire surface of the individual coal particles in a thin film, and permittingthe wax to congeal during cooling to normal room temperature to form a thin sealed coating of semisolid material on each individual and un'agglomerated particle. i

4. The method of protecting coal from dusting and oxidation which comprises subjectingthe coal to a bath containing in a carrying liquid a mixture of paraiiin waX with another viscous hydrocarbon which is semisolid at normal room temperature, the coating mixture being present in a proportion of from one per cent. to five per cent. the weight of the liquid, raising the temperature of the bath to a point materially higher than the melting point of the coating mixture to flow the coating mixture over the entire surface of the individual coal particles in a thin film, and permitting the coating mixture to congeal during cooling to normal room temperature to form a thin sealed coating on each individual and unagglomerated particle.

5. The method of protecting coal from dusting and oxidation which comprises subjecting the coal to a bath containing paraflin wax in a carrying liquid, the temperature of present in the proportion of from one per film, and permitting the wax to congeal during cooling to normal room temperature to form a thin sealed coating of semisolid material on each individual and unagglomerated particle.

7.-The method of protecting coal from dusting and oxidation which comprises subjecting the coal to a bath containing in a carrying liquid a mixture of p-arafiin wax with another viscous and neutral hydrocarbon which is semisolid at normal room temperature, raising the temperature of the bath to a point materially higher than the melting point of the coating mixture to flow the coating mixture over the entire surface of the individual coal particles in a thin film, and permitting the coating mixture to congeal during cooling to normal room temperature to form a thin sealed coating on each individual and unagglomerated particle.

8. The method of protecting coal from dusting and oxidation which comprises subjecting the coal to a bath containing in liquid suspension a coating material consisting wholly of viscous and neutral organic ingredients which are semisolid at room temperature, raising the temperature of'the bath to a point materially higher than the melting.

point of that ingredient of the coating material having the highest melting point to flow the coating material over the entire surface of the individual coal particles in a thin film, and permitting the coating material to congeal during cooling to normal room temperature to form a thin and uniform sealed coating on each individual and unagglomerated particle.

In testimony whereof I have hereunto set my'hand.

. HARVEY R. FIFE.

the bath being materially higher than the melting point of the wax to flow the wax over the entire surface of the individual coal partlcles in a thin film, and permitting the wax to congeal during cooling to normal"