US2923033A - Method for pelleting - Google Patents

Description

2,1960 w. R. BALDWIN ETAL 2,923,033

METHOD FOR PELLETING Filed Sept. 24, 1954 's Sheets-Sheet 1 STM. IN STM. OUT

WARREN R. BALDWIN J AM ES N. BOH N INVENTOR.

AGENT.

Feb. 2, 1960 w. R. BALDWIN ETAL 2,923,033

METHOD FOR PELLETING Filed Sept. 24, 1954 .3 Sheets-Sheet 2 WARREN R. BALDWIN JAMES N. BOHN INVENTOR.

AGENT Feb. 2, 1960 w. R. BALDWIN ETAL 2,923,033

METHOD FOR PELLETING Filed Sept. 24, 1954 3 Sheets-Sheet 3 WARREN R; BALDWIN JAMES N. BOHN v INVENTORS AGENT.-

United States Patent O METHOD FOR PELLETING Warren R. Baldwin and James N. Bohn, Kenvil, N.J., assignors to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Application September 24, 1954, Serial No. 458,231

9 Claims. (Cl. 18--47.2)

This invention relates to forming pellets from fusible materials and more particularly relates to the formation of pellets from fusible explosive material.

Although a large number of processes and considerable apparatus are available for forming pellets from fusible materials, it has been found that no apparatus or process known will produce large quantities of pellets having satisfactory configuration without a large outlay for complicated and expensive equipment which does not require close control throughout the pelleting operation. Basically, most of the processes employed for pelleting fusible materials, and in particular fusible explosive materials such as trinitrotoluene, provide a means for melting the material and then introduce the molten material into a vessel having a perforated bottom or a bottom equipped with a plurality of nozzles. The molten liquid then drips through the perforations or nozzles and the droplets fall through an air shaft or into a catch tank of an immiscible liquid to cool and solidify. In fact, for experimental purposes it is quite possible to obtain trinitrotoluene pellets of sorts by merely forming nail holes in the bottom of a tin can, holding the can over a pail of water and pouring molten trinitrotoluene or other material into the can at a rate which will produce droplets through the perforations. Upon striking the liquid and sinking, the droplets solidify. It is apparent, of course, that such equipment is not practical for plant operation even if constructed on a large scale. In order to obtain droplets of the desired size through a given perforation, the rate of flow of molten material to the dropping vessel or the liquid head above the perforation is critical. Thus, in many prior art processes, expensive and complicated control devices are employed which either meter the flow of molten material to the perforations or else maintain a constant liquid head above the perforations. If the flow is too great or the liquid head is too high, the molten material will stream from the perforations rather than issue forth as droplets. Depending upon the particular material employed, such streams either solidify as cords or else break up upon striking the cooling bath and form an undesirable amount of fines.

At the present time there has arisen considerable demand for pelleted trinitrotoluene or similar fusible explosive for use in blasting operations. The trinitrotoluene employed is available either in newly manufactured flake form or else in chunks of various sizes from military scrap. It is therefore highly desirable to the explosives art to have available a simple pelleting apparatus and process whereby trinitrotoluene and other fusible explosive materials in the varying sizes available may be easily and economically converted into pellets of the desired size.

Now in accordance with the present invention, fusible materials such as trinitrotoluene may be melted and con verted into pellets of the desired size by means of simple inexpensive apparatus and with a minimum of control and supervision. In general, the invention relates to a pelleting apparatus for fusible materials having in com bination a tank to contain an immiscible cooling liquid at a predetermined liquid level, a vessel to receive the solid, fusible material, the bottom of which is perforated and is disposed above the liquid level in the tank, and heating means associated with the vessel to apply heat adjacent the bottom of the vessel to melt only that fusible material which is adjacent the bottom of the vessel. Preferably, the tank will be a metal receptacle of suitable size and suitably equipped with means for removing the pellets formed. If a batch type process is to be employed, the tank may be equipped with an outlet in or adjacent the bottom thereof in order that the entire charge of cooling liquid and pellets may be removed at the end of each run. If a continuous process is desired,- siphoning or jetting means may be provided in conjunction with suitable liquid supplying means to maintain the level and temperature of the liquid in the tank as desired.

The melting vessel will preferably be a metallic pan, the bottom of which is provided with perforations of the desired size. Preferably, the perforations will be disposed in spaced rows. The vessel is equipped with heating means which will melt only the explosive in the bottom of the pan adjacent the perforations. Such heating may be obtained in various ways such as by the provision of a jacket through which a fluid heating medium may be circulated. Alternatively, electrical heating means may be employed at the bottom of the vessel. However, it is preferred to employ a small steam pipe between each of the rows of perforations and connecting these pipes to an inlet and an outlet header at opposite ends of the rows of perforations. These steam pipes may be disposed within the melting vessel or else may be attached to the bottom of the melting vessel. Preferably, the pipes will be disposed within the vessel and will either contact the vessel bottom or be disposed in close spaced relation with the bottom of the vessel.

In employing the apparatus of the invention the fusible material is introduced into the melting vessel in solid form. Heat is then applied adjacent the bottom of the vessel which is suflicient to melt only the exposive which is adjacent the bottom of the vessel. As the material melts, the molten liquid drips through the perforations and into the catch tank disposed below. As the fusible material melts, fresh unmelted material progresses downwardly in the vessel to the zone adjacent the heating means where melting is effected. Thus, there is no substantial liquid head and the intricate control means heretofore employed are unnecessary. The speed at which the melting is eflected in the bottom of the vessel may be readily controlled by the temperature of the heating material passing through the jacket or through the pipes as the case may be, or by means of a rheostat if electrical heating is employed. If desired, a hopper of any desired size may be employed above the melting vessel and filled with the solid fusible material to be pelleted. As indicated, the apparatus may be employed in a batch or continuous process and the pelleting process may be started up or shut down merely by turning otf the heating means disposed in or about the bottom of the melting vessel.

Having generally described the invention, a specific embodiment will now be discussed with reference to the accompanying drawing which illustrates apparatus particularly designed for the pelleting of flake or chunk trinitrotoluene but which may be employed in pelleting other fusible materials. In the drawing, Fig. 1 is a diagrammatic view of the entire apparatus, Fig. 2 is a plan view of the melting vessel including steam pipes and headers disposed on the vessel bottom, Fig. 3 is a sectional view of the melting vessel, and Fig. 4 is the plan view of Fig. 2 except that the steam pipes and headers are disposed under the bottom of the vessel.

In the drawing, in which like parts are referred to by like symbols, the melting vessel 10 is formed with hollow walls into which steam may be admitted through inlet pipe 11 and removed through outlet pipe 12. The bottom of the vessel 10 contains a grid-like framework of steam pipes 13 connected at one end to inlet header 14 and at the other end to outlet header 15. Steam is admitted to header 14 through inlet pipe 16 and is removed from outlet header 15 through outlet pipe 17. Spaced rows of perforations 18 are disposed between the steam pipes 13. The steam pipes 13 and headers 14 and 15 may be disposed under the bottom of the vessel 10 as illustrated with reference to Fig. 4. The elements 13', 14, 15' 16' and 17 of Fig 4, all below the vessel bottom (dotted lines) are otherwise the same as those correspondingly numbered parts (unprimed) of Fig. 2. In the trinitrotoluene pelleting operation to be described, these perforations were punched through the bottom of the vessel 10 and were inch in diameter. The melting vessel 10 is suspended by means not shown over column of water in cylindrical tank 19. In the operation to be described, the bottom of the melting vessel is disposed 1% inches above the water level in the tank 19. An inlet 20 is provided near the top of tank 19 for admission of water or other quenching liquid to the tank. A hose 21 leads from the bottom of the tank 19 and is employed for removal of liquid and pellets.

Employing the apparatus similar to that shown in the drawing and as above described, trinitrotoluene was formed into dense regular pellets having a diameter of about A; inch. In this operation, the melting vessel was made of copper sheeting .032 inch thick and the vessels bottom was 2 feet square. Holes 4; inch in diameter were punched on /2 inch centers in rows 1 inch apart. The pipes 13 were made from copper tubing having an outer diameter of 4 inch and rested on the bottom of the vessel.

A charge of 200 pounds of flake trinitrotoluene was dropped into the melting vessel and the catch tank was filled with water to within 1% inches of the base of the vessel. Five-pound steam (108 C.) was introduced into the header 14 through inlet pipe 16 and exhausted through outlet header and outlet pipe 17. The water in the tank was at a temperature of 65 F. when operations were begun. The trinitrotoluene adjacent the steam pipes 13 melted and the solid trinitrotoluene settled in the pan to replace the molten trinitrotoluene which dripped through the perforations and dropped into the water in the catch tank. The pellets solidified as they dropped through the Water in the tank and accumulated in the bottom. When all of the charge of flake trinitrotoluene had become molten and passed through the perforations, the pellets formed were removed through the hose 21 and placed on trays, each tray containing about pounds of pellets. The pellets were spread out and the pans were placed in a drying room where the temperature was maintained at about 140 F. until the pellets were dried (about 2 hours). The resulting pellets were spheroidal in form with only about 2% passing through a 12 mesh screen. The pellets had a bulk density of 0.945 and a specific gravity of 1.62. The pellets were formed in the operation described at a rate of 500 pounds per hour.

It has been found that when pelleting trinitrotoluene with the apparatus described and illustrated, it is desirable that the bottom of the melting vessel be not less than /2 inch and not more than 4 inches from the liquid level in the catch tank. Where the bottom of the vessel is less than /2 inch from the water, some difiiculty was encountered with splashing. When the distance was greater than 4 inches, some difficulty was obtained with the breaking up of the droplets from the perforations into fines which, for the desired use in blasting operations, were undesirable.

In the run described, no steam was circulated through the walls of the melting vessel. It has been found that actually the jacketing of the melting vessel is unnecessary, although the use of additional heat may sometimes be desirable in speeding up the melting in the vessel where a large charge is employed or where larger pellets are desired which necessitate the use of perforations of greater diameter. In pelleting trinitrotoluene it is preferred to employ steam having a temperature between and C. With all explosives, it is desired to use a steam temperature which will maintain the molten material just above its freezing point. It is desired also that the water or other liquid in the quench tanks be maintained at a temperature between 50 and C.

While the invention has been specifically illustrated with trinitrotoluene (M.P. 80.5 C.), the process and apparatus of the invention are equally operable with any material which can be safely melted and will solidify by being dropped into a liquid which is immiscible with the molten material. Preferably, of course, the liquid should not be a solvent for the solidified pellet. Other low melting crystalline explosive materials which may be pelleted in accordance with the invention include diethanolnitraminedinitrate (M.P. 51 C.), dipentaerythritol hexanitrate (M.P. 75 C.) and picric acid (M.P. 122 C.). Good results have also been obtained with Cyclotol (mixture of trinitrotoluene and cyclonite). The finely divided cyclonite is not melted but is carried through the perforations by the trinitrotoluene and is dispersed in the solidified droplets.

In some instances it may be desirable to employ a wetting agent in the liquid in the catch tank in order to prevent or minimize the formation of a scum on the surface of the liquid. In pelleting trinitrotoluene it has been discovered that if such a scum forms, the regularity of the size of the pellets is adversely affected. Examples of operable wetting agents include dioctyl sodium sulfosuccinate, polyethylene glycol tert-dodecylthioether, and sorbitan monolaurate. Preferably the wetting agent will be employed in amounts such that it will constitute from .01 to .05 of the liquid in the tank.

It has further been found that the temperature of the water or other liquid in the catch tank is not especially critical as long as the temperature is maintained substantially below the solidification point of the material being pelleted. At the higher temperatures greater travel through the liquid is required to solidify the droplet and form a pellet, thus necessitating greater liquid depth in the tank. It the case of trinitrotoluene, for example, it was found that the droplets were fully solidified after passing through 2 feet of water maintained at 65 F. while about 5 feet of water was required when the temperature was raised to F. As indicated, in a continuous process means may readily be provided to continuously add cold water and thus maintain the temperature at the desired level. In the batch process specifically described, the water in the tank was changed each time a 200 pound charge of flake trinitrotoluene was pelleted.

As indicated, it is not necessary that the trinitrotoluene be finely divided prior to introduction into the melting vessel. Excellent results were obtained when lump trinitrotoluene having a particle size of about 2 inches by 5 inches was charge into the melting vessel. The use of larger particles requires use of somewhat higher steam temperatures to maintain the desired rate of production.

It will be seen therefore that the apparatus and process described is characterized by a number of important advantages, especially when employed in pelleting explosive materials such as trinitrotoluene. In the first place, apparatus such as that specifically described is inexpensive and is easy and safe to operate. Still even this small unit will produce 4000 pounds of pellets in an 8 hour shift. From the standpoint of control, hardly any supervision is necessary. Feeding of solid fusible material is by gravity flow and rate of flow is dependent upon steam temperature or the temperature of any' other heating means employed. Since only that material adjacent the bottom of the melting vessel is melted, the amount of molten explosive is always small. Moreover, since there is no separate melting pot or conduits in which the material must be held at temperatures substantially above the point of solidification, the fusible material in the invention is substantially at the freezing point when it passes through the perforations. Thus, instantaneous solidification is obtained when contact is made with the liquid in the catch tank.

Since variations of the invention other than those specifically described will be apparent to those skilled in the art, the invention is to be limited only by the scope of the appended claims.

What we claim and desire to protect by Letters Patent 1. A process for pelleting a fusible crystalline explosive material which comprises introducing the said material in solid form into a vessel having a perforate bottom; applying heat to said vessel, in amount sufiicient to melt only a portion of said material therein, at least at points adjacent the vessel bottom to melt a portion of said material adjacent said vessel bottom independently of application of heat to said vessel at any other point; receiving the resulting droplets of fused explosive material, issuing from the said perforations, in a liquid immiscible with the said droplets; and maintaining the said immiscible liquid at a temperature at which the said droplets solidify therein.

2. A process in accordance with claim 1 in which said fusible material is particulate and is continuously added to the vessel and the resulting solidified droplets are con tinuously removed from the liquid.

3. In a process in accordance with claim 1, applying heat to the walls of the vessel to a degree sufficient to melt only a portion of said explosive material adjacent the wall thus heated.

4. A process for pelleting trinitrotoluene which comprises introducing particulate, solid trinitrotoluene into a vessel having a perforated bottom, passing steam through conduits disposed adjacent the bottom of the vessel at a temperature sufficient to melt only the trinitrotoluene adjacent the conduits and the vessels bottom, catching the droplets of fused trinitrotoluene issuing from the perforations in a tank of water, and maintaining the water at a temperature at which the droplets solidify.

5. A process in accordance with claim 4 in which the steam is introduced into the conduits at a temperature between and C.

6. A process in accordance with claim 4 in which the Water is maintained at a temperature of between 50 and F.

7. A process in accordance with claim- 4 in which the particulate trinitrotoluene is continuously added to the References Cited in the file of this patent UNITED STATES PATENTS Tatham Feb. 12, 1878 231,489 Holtz Aug. 24, 1880 1,393,383 Linebarger Oct. 11, 1921 1,612,167 Beardsley Dec. 28, 1926 1,932,499 Woods Oct. 31, 1933 2,570,423 Batchelder Oct. 9, 1951 2,574,357 Stammer Nov. 6, 1951 2,666,948 Guenther Jan. 26, 1954 2,712,621 North July 5, 1955

Claims (1)

1. A PROCESS FOR PELLETING A FUSIBLE CRYSTALLINE EXPLOSIVE MATERIAL WHICH COMPRISES INTRODUCING THE SAID MATERIAL IN SOLID FORM INTO A VESSEL HAVING A PERFORATE BOTTOM, APPLYING HEAT TO SAID VESSEL, IN AMOUNT SUFFICIENT TO MELT ONLY A PORTION OF SAID MATERIAL THEREIN, AT LEAST AT POINTS ADJACENT THE VESSEL BOTTOM TO MELT A PORTION OF SAID MATERIAL ADJACENT SAID VESSEL BOTTOM INDEPENDENTLY OF APPLICATION OF HEAT TO SAID VESSEL AT ANY OTHER POINT, RECEIVING THE

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