GB2040217A

GB2040217A - A process and apparatus for producing and accelerating pellets

Info

Publication number: GB2040217A
Application number: GB8000737A
Authority: GB
Original assignee: Leybold Heraeus GmbH
Current assignee: Balzers und Leybold Deutschland Holding AG
Priority date: 1979-01-15
Filing date: 1980-01-09
Publication date: 1980-08-28
Also published as: GB2040217B; DE2901421A1

Abstract

For producing and accelerating pellets of frozen material, a starting material 2 is forced in the form of a continuous strand through a nozzle 4 into a lateral opening 7 of an element 6 rotatably arranged about an axis substantially normal to the nozzle axis whilst the opening 7 is approximately coaxial with the nozzle axis. On further rotation of the rotating element 6 the small section of the strand situated in the opening is separated and a pellet 13 is thus formed and is fired from an outlet opening 9 with the aid of pressurised gas admitted through a pipe 11. <IMAGE>

Description

SPECIFICATION A process and apparatus for producing and accelerating pellets The invention relates to a process for producing and accelerating pellets of frozen material and to an apparatus for carrying out this process.

Pellets of frozen material, such as hydrogen or deuterium, can be used to generate plasmas in the focal point of focussed high-energy laser and electron beams, for charging fuel in arrangements for investigating controlled nuclear fusion, and also in future fusion reactors. When carrying out such experiments the pellets have to be transported from their production site to the reaction site, which is some distance therefrom. German Offenlegungsschrift 2 611 314 discloses a process and an apparatus forming the pellets wherein the starting material is forced in the form of a continuous strand through a nozzle, and after the strand has left the nozzle the pellets are formed by removing small sections from the strand and the pellets thus formed are then accelerated in free fall to the reaction site.

The disadvantage of this is that the velocity of the pellets at the reaction site cannot be taken into account since the fall acceleration is always constant. A further disadvantage is the fact that the device for producing the pellets must always be arranged above the reaction site. Finally, the scatter with which the pellets strike the reaction site is relatively large since the pellet-separation device does not always operate uniformly.

The object of the present invention is to provide a process and an apparatus for producing and accelerating pellets according to which it is possible to transport the pellets with a higher degree of accuracy to the reaction site. In addition, it is intended that the velocity of the pellets at the reaction site and the production rate should thereby be able to be adjusted.

This object is achieved in accordance with the invention in a process for producing and accelerating pellets of frozen material, which comprises forcing the material in the form of a continuous strand through a nozzle and into a lateral opening in an element rotatable substantially normal to the nozzle axis whilst the opening is approximately coaxial with the nozzle axis, further rotating the rotating element to separate the section of the strand situated in the opening and thus form a pellet, and accelerating the pellet from the opening with the air of a pressurised gas.

With a process of this type the step of producing the pellet is separated from the step of accelerating the pellet, with the result that the formation of the pellets no longer has any effect on the direction of acceleration. This ensures that the scattering with which the pellets strike the reaction site is extremely small. By altering the rotational velocity of the element and by altering the working pressure of the pressurised gas serving for the acceleration, both the production rate and the velocity in the reaction site can be influenced. In this connection it is particularly advantageous that, as has recently become increasingly desirable, pellets can be produced having extremely high velocities, e.g. several thousand metres per second.

It has, of course, already been proposed to accelerate pellets using a iight gas cannon (see D.

Dimock et al.: "Pellets Acceleration Studies Relating to the Refueling for Steady-state fusion Reactor"; Danish Atomic Energy Commission, Ris Report No.

332, 1975). The procedure in this case is to cool a flat plate to the required temperature by means of a cryogenic apparatus specially designed for this purpose. The flat plate has a bore in which the pellet material is frozen solid by the addition of gas. The plate is then moved so that its bore together with the pellet is situated in the barrel of the gas cannon. The disadvantage of this is that the aforedescribed condensation method does not guarantee that the pellet material will fill all the space provided for this purpose. Depending on the conditions (pressure, temperature and temperature gradient) during the condensation of the starting gas, it is found from experience that various forms of the solid starting gas, e.g. snow-like or partially compact with fairly large hollow spaces, are obtained.If the pellets have a non-compact shape this means that the subsequent acceleration using the gas cannon is not always uniform, and a large scattering of the pellets at the reaction site again occurs.

In constrast, the solution according to the invention has the advantage that the highly developed extrusion technology, which has been successfully used for industrial purposes and is favourably priced, can be utilised, and accordingly the extrusion of the pellet material into the opening of the rotatable element provided for this purpose guarantees a uniform compact shape of the pellets that fills the whole predetermined space, whereby an essential prerequisite for a uniform and effective acceleration in accordance with the principle of the gas cannon is met.

The invention also provides an apparatus for carrying out the process which comprises means for extruding a continuous strand of pellet starting material through a nozzle in a housing containing a rotatable plug element having at least one lateral opening therein adapted to be aligned with the nozzle in a predetermined rotational position of the plug, a pellet outlet opening in the wall of the housing angularly separated from the nozzle and disposed to align with the opening in the plug in a further rotational position of the plug, and means for admitting pressurised gas to the opening in the plug when so aligned.

Further advantages and details of the invention will be described in more detail hereinafter with reference to the accompanying drawings in which a number of embodiments of the invention are illustrated diagrammatically. In the drawings: Figure 1 is a cross-sectionai elevation of one embodiment of the apparatus; Figure 2 is a cross-section elevation of the apparatus of Figure 1 with the plug element rotated; Figures 3 and 4 are views respectively similar to Figures 1 and 2 of a second embodiment of the apparatus; Figures 5 and 6 are views respectively similar to Figures 1 and 2 of a further embodiment of the apparatus; and Figure 7 is a cross-sectional elevation of 90 of the apparatus of Figure 5.

All the embodiments include an extruder pipe 1, in which the pellet starting material 2, e.g. frozen gas, is located. The necessary cooling devices or cryostats are not shown for the sake of clarity. Such devices are described in German Offenlengungsschrift 2 611 314.

The pellet starting material 2 is forced by means of a die 3 through a nozzle 4 into the interior of a housing 5 in which an element 6 is rotatably arranged in the manner of a taper plug, the element 6 having a lateral opening 7 coordinated with the nozzle 4. The housing 5 has in each case, as an extension of the nozzle 4, an opening 8 through which the excess pellet starting material can leave in a downward direction.

In the embodiment according to Figures 1 and 2, the rotatable element 6 is cylindrical. The lateral opening 7 coordinated with the nozzle 4 is formed as a continuous bore. The drive means and control means for the rotatable element 6 are not shown in detail. If the rotatable element 6 is in the position shown in Figure 1 in which the nozzle 4 and the bore 7 are coaxial, pellet starting material will then pass into the bore 7. Extrusion is then preferably carried out until the whole bore 7 is reliably filled. The rotatable element 6 then adopts a position as shown in Figure 2. In this position the bore 7 is coaxial with further openings 9 and 10 provided in the housing 5.

Pressurised gas is then fed, in a manner not described in more detail, into the opening 10 via a connecting piece 11. The opening 9 serves for the outlet of the pellets, and is coordinated with a barrel 12 in the manner of a gas cannon. It is clear that with the aid of pressurised gas fed through the connecting piece 11,the pellets 13 located in the bore 7 can be expelled and shot from the barrel 12. The velocity of the pellets leaving the barrel 12 depends on the working pressure of the pressurised gas. The pellet production rate depends on the rotational velocity of the rotatable element 6. The pellets 13 located in the bore 7 always have the same length, same diameter and same consistency, which accordingly ensures a uniform acceleration of pellets produced in sequence.

In the embodiment according to Figures 3 and 4 the rotatable element 6 is formed hollow. In order that the length of the pellets is again always constant, a stationary knife 14 is associated with the internal bore of the rotatable element 6. The size of the pellets produced thus depends on the diameter of the opening 7 and the wall thickness of the hollow rotatable element. The manner of production of the pellets and their acceleration from the barrel 12 corresponds to that of the embodiment according to Figures 1 and 2.

In the embodiment according to Figures 5, 6 and 7, the rotatable element 6 is likewise formed hollow.

However, this embodiment differs from that of Figures 3 and 4 in that the pressurised gas is not fed through a separate connecting piece 11 but through the similarly hollow formed rotation axis 15 (see Figure 7) of the rotatable element 6. In this way the number of necessary contacts between cold regions and regions at room temperature is restricted, and the thermal stress on the cryogenic apparatus is thus kept to a minimum. It is also clear from Figure 7 that the rotatable element 6 may be formed having an internal taper, whose diameter at the end closer to the gas feed is smaller than at the other end, with the result that during the supply of pressurised gas for accelerating the pellets the element 6 is forced into the internal housing 5, likewise conicaily shaped, and the gas-tight seal between the rotatable element 6 and the housing 5 is automatically increased.

Finally, in the embodiment according to Figure 7 two lateral openings 7 and 7' are provided, so that served pellets can be produced during one revolution of the element 6.

In all the embodiments the rotation axis of the rotatable element 6 is approximately normal to the axis of the nozzle 4. The barrel 12 of the gas cannon is likewise arranged approximately normal to the plane formed by the rotation axis and the nozzle axis.

Claims

.1 A process for producing and accelerating pellets of frozen material, which comprises forcing the material in the form of a continuous strand through a nozzle and into a lateral opening in an element rotatable substantially normal to the nozzle axis whilst the opening is approximately coaxial with the nozzle axis, further rotating the rotating element to separate the section of the strand situated in the opening and thus form a pellet, and accelerating the pellet from the opening with the axis of a pressurised gas.
2. An apparatus for carrying out the process according to claim 1, which comprises means for extruding a continuous strand of pellet starting material through a nozzle in a housing containing a rotatable plug element having at least one lateral opening therein adapted to be aligned with the nozzle in a predetermined rotational position of the plug, a pellet outlet opening in the wall of the housing angularly separated from the nozzle and disposed to align with the opening in the plug in a further rotational position of the plug, and means for admitting pressurised gas to the opening in the plug when so aligned.
3. An apparatus according to claim 2, including a tubular section associated in the manner of a barrel of a gas cannon with the pellet outlet opening outside the housing.
4. An apparatus according to claim 2 or 3, wherein the opening in the rotatable plug is a through opening, and the gas admission means are arranged at the side of the housing opposite the pellet outlet opening.
5. An apparatus according to any one of claims 2 to 4, wherein the rotatable plug element is hollow.
6. An apparatus according to claim 5, including a stationary knife associated with the internal wall of the hollow rotatable element in the region of the lateral opening.
7. An apparatus according to Claim 5 or Claim 6, wherein the pressurised gas is admitted via the axis of rotation of the hollow rotatable element.
8. An apparatus according to any one of Claims 2 to 7 wherein the rotatable plug is a tapered hollow plug.
9. An apparatus according to any one of claims 2 to 8, wherein the axis of rotation of the rotatable plug is normal to the axis of the nozzle, and a gas cannon formed by the pellet outlet opening, a barrel and the pressurised gas admission means is arranged normal to the plane defined by the rotation axis and nozzle axis.
10. An apparatus according to any one of claims 2 to 9, wherein the rotatable element has a plurality of lateral openings for forming pellets.
11. A process for producing and accelerating pellets of frozen material according to claim 1 and substantially as hereinbefore described.
12. Apparatus for producing and accelerating pellets of frozen material substantially as hereinbefore described with reference to the accompanying drawings.