US2349249A - Apparatus for the recovery of solvent - Google Patents

Description

May 23, 1944.

G. E. DESETTI ETAL APPARATUS FOR THE RECOVERY OF SOLVENT Filed May 14, 1941 4 M40811; BHMace INVENTORS ATTORNEY stantially PatentedMay 23, 1 944 Gild E. Desetti,-woodbnry, N. .l., and Walter A.

Dew, Bill H.

Mackey, and Richard G. Wood bridge, .Ir., Wilmington, du Pont de Nemours & Company, W

Del., assigncrs to E. I.

Del., a corporation of Delaware Application May 14, 1941, Serial No. 393,340

2 Claims.

This invention pertains to the recovery of solvent from smokeless powder, particularly with respect to an improved apparatus for the recovcry of said solvent. 4

The object of the present invention is an assembly adapted to the efficient removal of solventwhile permitting the production of a subuni'form powder. Another object is an apparatus adapted to facilitate control of the solvent vapor content of the drying medium during the solvent recovery treatment. A further object is a solvent recovery assembly adapted to the regulated removal of solvent from smokeless powder by controlling the solvent vapor content of the drying medium and the temperature of said drying medium as well as that of the powder being treated. Astill further object is an apparatus capable of use for all the steps involved in the finishing of powder, that is to say, solvent recovery, water drying, and air drying. Other objects will become apparent as the invention is described in detail hereinafter.

The foregoing objects are attained by means of the assembly shown in the accompanying drawing which illustrates preferred embodiments of the invention. Fig. 1 denotes a schematic plan of the various elements composing the assembly. Fig. 2 refers to. a cross-sectional view of the solvent recovery car along the line 2-2. Similar numerals refer to similar parts throughout the drawing,-

Referring to Fig. 1, the numeral I denotes an insulated powder container, said container preferably being constructed of welded metal and mounted on a chassis, so that facile transfer of the powder, together with its contents, can be effected whenever it is deemed desirable. Preferably, the inner part of the container is constructed of stainless steel, because this material permits the construction of inner surfaces which are smooth, and to which particles cannot cling. The outer surfaces of the car may be constructed of galvanized metal. Insulation may be effected by means of a number of well-known insulating materials. Glass wool has proved to be very attractice for this purpose. This insulated, metal container is provided with a screen, 2, said screen being adapted to support or retain the powder being treated while permitting passage of the treating medium-therethrough. The powder is introduced into the container by means of the openings I, said openings being provided with lids which maybe positioned readily and which in addition are designed to be made airor gas-tight by means of the liquid seal (shown welded the already cooled any desired ratio.

the condenser, the temperature of this part of the top of the at a point immediately before the heater,

in Fig. 2). The drying medium is introduced into the car through opening 4. .At this juncture, the line 5 is joined to the car and the iointure also made gas-tight by means of a liquid seal. After the powder has been treated it is removed from the container merely by opening up the hinged section I and shoveling it therefrom, or by tilting the car somewhat and permitting the powder to flow through said opening.

The direction of flow of the drying medium is indicated. It may be seen that the direction of flow of the gas is downwardly into the car, said flow being distributed uniformly throughout the bulk of the powder in the container by means also shown in Fig. 2, the flow of the gas-continuing on through the screen and exiting from underneath the screen, where it passes to the filter, 8. .The piping between the filter and car is connected to said car by means of a removable vapor-tight member, 6. The filter serves the purpose of removing any finely divided solid particles which may pass through the screen and which otherwise might cause damage to the assembly. Although various filtering media may be employed, we prefer to use glass wool, because this material has proved to be particularly emcacious and thus can be employed more advantageously than various types of paper or cloth. The desirable high rate of circulation. is attained by means of the blower, 9, said blower being of the type deemed safe for use with explosive gas mixtures. As shown, the gases passing through the filter enter the blower and pass therethrough. After leaving the blower, the drying medium is separated into predetermined portions, one pordirectly to the heater II, wherev tion being passed, as the remainder is passed through the condenser, II, and thence through the cyclone separator, l2. Separation or division of the gas from the blower is efiected by means of the valves or dampers, ll, these being manipulated to attain During its passage through the drying medium is cooled sufllciently to cause condensation of at least part of the solvent va-- pors "present. Further cooling is effected when cooled cyclone separator. This latter element is particularly effective with respect to the separe tion of entrainedsolvent droplets. The solvent condensed passes down through the line II, which is designed to prevent escape of gases, and then passes to storage. The residual gases exit from separator and pass into the .line

gases are passed into the mend is to be effected.

behind the valve, M. The passage of part of the gases through the condenser, of course, lowers the temperature of this portion of the gases and causes condensation of some of the solvent vapors present. The cooled gases of lower solvent content are then joined with the gases coming directly from the blower and the resultant mixture is passed into the heater where a predetermined temperature is maintained, this increase in temperature having the oflect of raising the solvent-carrying capacity of the gases. From the heater, the gases pass to the top of the powder container, and the circulation described above is repeated.

The details of construction of the powder car are shown in Fig. 2, wherein the numeral I! refers to the cover of the car. Said cover is preferably composed of two metallic layers, with a layer of insulatingmaterial thereinbetween. This cover merely rests over the insulated side walls, 22, of the car, and forms a vapor-tight union therewith by means of the liquid seal, l8, which is formed by cooperation of the lip of the cover with the curved member, 23. It will be noted that the liquid seal is entirely outside the car. This feature is advantageous because it prevents the introduction of water into the system as a result of evaporation of some of the water in the seal. No permanent connections or fastenings between the cover and the side walls of the car are employed, the

weight of the cover being suflicient per se to maintain a closed system. Thus, if accidental ignition of the powder or gases occurs, the cover is displaced so that the possibility of high pressure being created within the system is greatly re duced. Consequently, accidental ignition of the contents is usually characterized only by burning, rather than by explosion or detonation. The

members, [9, are employed for removal of the cover.

The cover is provided with quick opening lids, l5, which are made vaporor gas-tight by means of the liquid seal, I 6. Directly beneath the lid'l5. and extending almost the entire length of the car vis the baffle, 20. This member is provided with a multiplicity of perforations, and serves as a means for distributing the incoming gas over the entire bed of powder being treated, so that said gas may diffuse through the entire powder bed. Watersprays, 2|, are provided for wetting down the powder at the end of the solvent recovery treatment, in case it is desired to remove the powder at the end of said treatment.

The assembly described in the foregoing is employed for the recovery of solvent from smokeless powder in the followin manner. Freshly grained or green smokeless powder is loaded into the car at a locus which is at an appreciable distance from the place where the solvent recovery process During the loading operation, the major portion of the solvent vapors evolved may be condensed by passing them in contact with cooling coils. After the charge of the green powder has been introduced into the car, the various openings of the car are closed and then it is moved from the graining area to the solvent recovery area by means of a dinghy or other suitable engine provided for hauling such cars when they are superimposed on a chassis as described hereinbefore. This portable feature of the car is important because of the fact that it avoids concentration of large quantities of smokeless powder and explosive gas mixtures. The loaded car is then placed in proper position in the solvent recovery area and attachment of the line 5 in the proper position is made. The lids, l5, have already been clamped in a tight position and the water seal has been made. Likewise, attachment at the base of the car is made for the exit of the drying medium therefrom. The temperature of the heater and condenser has already been regulated so that when the operation is started, the air in the powder container is purged therefrom via the cyclone separator and then exact regulation of the air fiow is made.

The period of operation for the recovery of solvent is continued until potentially all of the solvent, in most cases ether and alcohol, which can be volatilized readily under the conditions obtaining, is removed. The present arrangement permits facile control of the temperature of the drying medium as well as its solvent carrying capac ity. This is due to the fact that the temperaturt and solvent content of the gases entering the cax can be controlled accurately without difficulty. These conditions may be varied so that practically any set of factors considered desirable during the various stages of the operation can be obtained. The length of time of treatment will vary according to the size of the powder grains, their composition, the conditions obtaining during treatment, etc.

The foregoing apparatusis particularly useful for the efficient removal of volatile solvent from newly made grains of smokeless'powder because it permits control of the solvent vapor content of the medium surrounding the powder and the tem perature of this medium as well as that of th-. powder. As a result, the rate of removal of the solvent can be controlled so that when subjected to the treatment; the dimensions of the grain will change uniformly, and controlled shrinkage will be achieved when the solvent is removed therefrom. In addition, it is adapted for use in processes involving what may be considered a high rate of circulation of the drying medium, this feature being particularly advantageous in view 01 the fact that a high fiow of the drying medium is conducive to the production of a uniform lot or powder. In other words, variations in solvent composition of the powder are reduced to a minimum.

It will be understood that the utility of the present assembly is not limited to the recovery of solvent from freshly-granulated or green smokeless powder. Instead, it may also be employed for the steps employed in the finishing of smokeless powders. These steps usually include preliminary air drying, water drying, and a final air drying treatment. The water-drying step involves steeping the powder in water at an elevated temperature, and is employed in order to reduce the volatile solvent in the powder to a satisfactory residual solvent content. After this has been accomplished, the powder is accorded final air drying, during which step the excess moisture in the powder is removed.

Thus, if the powder is to be accorded a preliminary air drying, it is necessary only to disconnect the pipe at the base of the powder car, employing the resulting opening for introduction of air, and closing the valve into the condenser so that this unit .as well as the separator is cut out of the system. As a result, air at room temperature comes into the piping, passes through the filter, blower, and heater, and then the warm airpasses downwardly into the car and through the powder bed, the moist air leaving the car at the exit resulting when the piping was disconnected. For the water-drying step, it is necessary only to provide an inlet and outlet for hot water of the desired temperature, and to plug the opening at the base of the car. Final air drying of the powder may be effected in the manner described above for the preliminary air drying treatment.

It will be understood that the assembly described herein is not limited to the use of one powder car. Instead two or more cars may be attached in parallel to the system, it being essential only that the various parts of the assembly be designed to yield the desired flow and temperature conditions. Insuch cases it is possible to recover simultaneously-the solvent from a plurality of batches of powder while preventing the concentration of an unduly large quantity of powder in one zone. This may be accomplished by simply providing a fire wall between the cars.

The process disclosed herein is claimed in copending application Serial No; 257,840, filed February 23, 1939, now Patent No. 2,280,803 of April 28, 1942.

It will be apparen to those skilled in the smokeless powder art that the foregoing description permits of variations, without departing from the spirit or scope thereof. We intend,

thereiorato be limited only in accordance with the following claims.

We claim:

1. An apparatus'for the treatment of smokeless powder comprising a powder container, a vapor entry and a vapor exit for said container, a conduit externally connecting said exit with said entry and connecting in series enroute a vapor filter, a blower, and a heater, and a by-pass leaving said conduit and returning to the same between said blower and heater, said by-pass connecting in series in turn a condenser and a separating means.

2. An apparatus for the treatment of smokeless powder comprising a powder container constructed as a detachable, movable vehicle, a vapor entry and a vapor exit for said container, a conduit externally connecting said exit with said entry and connecting in series enroute a vapor filter, a blower, and a heater, and a by-pass leaving said conduit and returning to the same between said blower and heater, said by-pass connecting in series in turn a condenser and a separating means.

GILD E. DESE'I'I'I. WALTER A. DEW. BILL H. MACKEY. RICHARD G. WOODBRIDGE, Ja.

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