US3711709A

US3711709A - Irradiation system

Info

Publication number: US3711709A
Application number: US00864691A
Authority: US
Inventors: W Rudolf
Original assignee: Sulzer AG
Current assignee: Sulzer AG
Priority date: 1968-10-10
Filing date: 1969-10-08
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16
Also published as: DE1803052C3; GB1281047A; DE1803052A1; FR2020285A1; CH497768A; JPS4926240B1; DE1803052B2

Abstract

The irradiation elements are disposed within a grid made of tubes and distributed across the cross-section of the vessel. The irradiation elements and tubes are oriented to obtain a uniform dose of radiation on the granular material passing through the vessel. The discharge hoppers and knife cylinders are arranged to achieve discharge rates therethrough commensurate with the radiation and flow resistance conditions.

Description

United States Patent Rudolf Jan. 16, 1973 IRRADIATION SYSTEM [56] References Cited [75] Inventor: Wolfgang Hubertus Rudolf, Win- UNITED STATES PATENTS terthur, Switzerland 1,817,936 8/1931 Supplee ..250/52 1 Assigneer Sulzer Brothers, ur, 2,279,810 4/1942 Amott ..250/43 Switzerland 3,527,940 9/1970 Balanca et a1. ..250/44 3 6 [22] I Filed: Oct. 8, 1969 ,3 0,646 12/1967 Reiback et al 250/44 [21] Appl. No.: 864,691 Primary Examiner-William F. Lindquist Azt0rneyl(enyon & Kenyon Reilly Carr & Chapin [30] Foreign Application Priority Data ABSTRACT l l l Oct 968 Swmer and 15 33/68 The "radiation elements are disposed w1th1n a grid 52 US. Cl. .250 44, 21 102, 99 218, made tubes and distributed cmss'secflon 1 l 25/0/52 of the vessel. The irradiation elements and tubes are 511 int. c1. ..G0ln 21/26 (Timed (main a radiation [58] Field of Search "990, 218 249, 253; 21/9], granular material passing through the vessel. The

discharge hoppers and knife cylinders are arranged to achieve discharge rates therethrough commensurate with the radiation and flow resistance conditions.

13 Claims, 10 Drawing Figures PATENTEDJAH 16 I973 My 1 OF 3 3,711,709

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PATENTEDJAH 16 I973 3,711,709 SHEET 2 [1F 3 PATENTEDJAHIB 1975 SHEET 3 OF 3 3,711,708

Inventor.-

F y m 3:... w ma rc w mi? N A #w W a W v 6 IRRADIATION SYSTEM This invention relates to an irradiation system. More particularly, this invention relates to an irradiation system for a flowing material, and particularly for granular material.

It has been known to treat granular material, for example, cereals, with gamma rays by continuously passing the material through a vessel in-which radiation sources are disposed substantially along the longitudinal axis of the vessel to irradiate the material approximately in the radial direction. In some instances, due to the exponential reduction in radiation intensity with increasing distance from the radiation sources, the vessel has been subdivided into several annular chambers by means of concentric circular cylindrical shells and the flow rate of the material in the individual annular chambers has been reduced with an increasing distance from the longitudinal axis of the vessel. Accordingly, the radiation dose received by any one grain has not depended on which of the annular chambers it traverses.

Although, in theory, such an axial arrangement of the radiation source should provide an optimum efficiency, it is in practice relatively poor. This is because the circular cylindrical shells, having to withstand a large and irregular lateral pressure and having thus to be constructed of sufficient strength to withstand the pressure, absorb a large proportion of the radiation. Moreover, regulation of the flow rate of the individual annular chambers requires complicated regulating means. It has also been found that a large proportion of the material is subjected to severe shear stresses by the known discharge means and is thus crushed.

Accordingly, it is an object of the invention to optimize the efficiency of an irradiation system for flowing materials.

It is another object of the invention to utilize a simple regulating means to control the flow rate of granular material through an irradiated vessel.

It is another object of the invention to minimize the amount of radiation absorbed by the walls of a vessel through which material flows during irradiation.

It is another object of the invention to provide a simple irradiation apparatus.

It is another object of the invention to reduce mechanical stresses on the material flowing through an irradiated vessel.

Briefly, the invention provides an irradiation system having a vessel for directing a flow of material, particularly granular material, therethrough, irradiation members and means for obtaining a substantially constant flow of material through the vessel.

The irradiation members are disposed in a pattern substantially perpendicular to the flow direction of the material and extend over the cross section of the vessel so as to irradiate the vessel mainly along the longitudinal axis of the vessel while the radiation dose is distributed substantially uniformly across the vessel crosssection. The irradiation direction of the irradiation members is also oriented substantially upstream and/or downstream of the material flow. In order to distribute the irradiation elements across the vessel, a grid formed of hollow tubes is utilized with the tubes oriented in a pattern to obtain the uniformity of radiation dosage.

The means to obtain a constant flow of material includes a feeding means at one end of the vessel for introducing granular material into the vessel and a discharge means at the other end for removing the irradiated material from the vessel. The discharge means is formed of a plurality of part discharge means which are spaced across the cross-section of the vessel and are each operated so as to discharge a part flow of material at rates commensurate with the irradiation and flow resistance conditions of the material. Such part discharge means utilize knife cylinders of various constructions to achieve the desired discharge rates.

These and other objects and advantages of the invention will become more apparent when taken in view of the following detailed description and accompanying drawings in which:

FIG. I illustrates a longitudinal sectional view of an irradiation system according to the invention;

FIG. 2a illustrates a side view of a knife cylinder utilized in a part discharge means of the invention;

FIG. 2b illustrates a front fragmentary view of the knife cylinder of FIG. 2a;

FIG. 3a illustrates a plan view of the discharge means of FIG. 1;

FIG. 3b illustrates a view taken on line 3b-3b of FIG. 3a;

FIG. 4a illustrates a plan view of a modified discharge means according to the invention;

FIG. 4b illustrates a view taken on line 4b-4b of FIG. 4a;

FIG. 5 illustrates a plan view of a grid according to the invention;

FIG. 6 illustrates a longitudinal sectional view of a modified vessel according to the invention; and

FIG. 7 illustrates a side view of the mounting of an irradiation element in a modified grid according to the invention.

Referring to FIG. ll, the irradiation system includes a once-through concrete flow vessel ll of rectangular cross-section which has a lining 2 of stainless steel and a grid 3 disposed approximately at mid-height of the vessel 1. The grid 3 is formed of parallel irradiation members 5 which are supported on opposite sides in the vessel wall 4 across the cross-section of the vessel. The irradiation members '5 comprise a tube 6 in which commercial irradiation elements, for example Cobalt- 60 rods are serially and adjacently disposed (FIG. 5). The vessel 1 is thus irradiated mainly along its longitudinal axis in the upward and downward direction. Each tube 6 adjoins a duct (not shown) in the vessel wall by means of which, and during operating intervals of the system, the irradiation elements are retracted by means of a cable. Spent elements may also be exchanged for fresh elements through such ducts. In order to prevent small quantities of the material to be irradiated from remaining on the tubes 6 thus receiving a dangerous excess radiation dose, the tubes 6 are provided with an inclined cover 7 at the upper surfaces. The covers 7 thus serve to ensure passage of the particles through the grid 3. The irradiation members may also be staggered in the vertical direction in order to minimize any flow restriction.

The vessel l is provided with a feeding means 10 at the upper end and a discharge means 11 at the lower end for the material. The feeding means It) comprises a hopper i2 and a conveyor belt 13 which feeds material such as granular material into the vessel 1. The discharge means 11 extends over the entire cross section of the vessel 1 and includes part discharge means 14, 15, 16, 17 which extend in parallel to the

vessel walls

18 and 19. Each part discharge means comprises a hopper 20, 21, 22, 23 of rectangular cross section and an associated

knife cylinder

24, 25, 26, 27 respectively. The discharge flow zone of each part discharge means is bounded by two circular curvilinear plates, such as, 30 and 31 between the respective hoppers and knife cylinders. Each knife cylinder comprises a cylinder 32 and radially orientated plates or knives 33 which are uniformly distributed over the cylinder circumference and extend over the entire length of the cylinder 32. The outer edges 34 of the knives 33 extend in parallel to the circumferential lines of the plates 30, 31. The knife cylinders are driven by a common motor (not shown) at the same rotational speed. In operation, the rotation of the knife cylinders causes the pockets 35 formed by adjacent knives 33 to first be filled with irradiated materials and then to be discharged during rotation into a common hopper 40. A conveyor belt 41 is disposed beneath the hopper 40 to receive the material dropping from the hopper 40 so as to deliver the material out of the vessel 1. The quantity of material removed from the vessel is proportional to the rotational speed of the knife cylinders.

In operation, the conveyor belt 13 of the feeding means 10, driven by a motor 42, continuously feeds the material into the vessel 1. The flowing material is then irradiated upstream and downstream by the irradiation members of the grid 3 and removed from the vessel 1 by the discharge means 11. For a given discharge rate, that is, for a given rotational speed of the motor for the knife cylinders 24-27, the speed of the belt 13 is regulated to a constant filler level by means of a contents gauge 43 and regulating means 44 on the side wall of the vessel 1 as shown which influence the output of the motor 42.

.The tubes 6 of the grid 3 are arranged so that the radiation intensity of the grid 3 in the zone of the two vessel walls in which the irradiation members 5 terminate and which extend perpendicularly to the knife cylinders is less than in the central zone of the grid 3. Thus, the

knife cylinders

24, 25, 26, 27 are so constructed that the quantity of material delivered thereby is less near these walls than in the center zone of the cross section of the vessel 1. Accordingly, the radiation dose of the material passing the grid 3 near said walls is the same as the radiation dose in the central zone of the cross section where the radiation intensity is greater but the flow rate is also greater. To this end, the knife cylinders are provided with displacement members which reduce the volume of the pockets towards the vessel walls. For example, referring to FIGS. 2a and 2b, a knife cylinder having a pocket 50 between a pair of

adjacent knives

51, 52, as above, is provided with a displacement member 53 in the pocket 50 which reduces the capacity of the pocket 50 by the amount of the volume of the member 53. A suitable grading of the displacement member 53 causes its volume to increase gradually towards the two ends of the knife cylinder (FIG. 2b) so that the capacity of the remainder of the pocket becomes correspondingly smaller. The quantity delivered by such a knife cylinder is thus less in the zone of the two vertically extending vessel walls than in the central zone of the vessel.

Further, the radiation intensity near the two vessel walls 18, 19 (FIG. 1) is also less than in the remaining part of the grid, where the radiation of two members each becomes additive. Thus, it is necessary for the knife cylinders disposed near the

walls

18, 19. to be constructed for a smaller delivery rate than the knife cylinders disposed in the central zone of the vessel cross section. For example, as shown in FIGS. 3a and 3b, the diameters of the cylinders 60 and the displacement member 61, 62 of the two

central knife cylinders

63, 64 are smaller than the diameters of the cylinders 67 and the

displacement members

68, 69 of the two

outer knife cylinders

70, 71. However, the spacing between the axes of the

cylinders

63, 64, 70, 71 remains constant. Accordingly, the throughput in the zone of the

parallel vessel walls

18, 19 is less than in the central zone of the vessel cross section and the radiation dose of the material flowing in the various cross sectional zones is uniform.

Referring to FIGS. 4a and 4b, alternatively in order to obtain the throughout pattern of the material, the cylinders 72 and the displacement members 73, 74 mounted thereon can be of the same size for all knife cylinders. However, the knife cylinders in the central zone of the vessel cross section are disposed more closely adjacently than near the

walls

18, 19; The distance a between the axes of the middle knife cylinders 75, 76 is smaller than the distance b between the axes of the outer cylinders 77, 78 and the middle cylinders 75, 76. The quantity discharged in the central zone of the cross section is therefore greater than near the wall and the radiation dose received by the material is therefore uniform over the cross section.

Referring to FIG. 5, in order to improve the uniformity of the radiation dose over the cross section of the vessel 1 still further it is possible, on the one hand, for the irradiation members in the grid to be disposed more closely adjacently relative to the parallel extending

vessel walls

18, 19 and, on the other hand, for the radiation elements disposed in the irradiation members to be disposed more closely adjacently relative to the perpendicularly extending vessel walls. In this case, the

outer irradiation members

80, 81 of the grid 82 are disposed near the

parallel vessel walls

18, 19 but more closely adjacently than the irradiation members 83, 84 in the central zone of the grid. The outer radiation members 85, 86 in each tube are also disposed more closely adjacently than the

radiation elements

87, 88 in the central zone of the grid. The resultant radiation distribution therefore becomes more uniform over the entire grid.

Referring to FIG. 6, in order to maintain a oncethrough flow vessel which is loaded in an intermittent manner as by a bucket means, as shown, filled at a constant level, the vessel 100 is provided with an integral hopper 101 atthe upstream end. This hopper 101 can be periodically fed and thus can function as a buffer volume. A'shielding member 103 is disposed downstream of the discharge. opening 102 of the hopper 101 in order to prevent material stored in the hopper 101 from being prematurely exposed to radiation. When the discharge means 104 (which is constructed as above) of the once-through flow vessel 100 is in operation, the material will leave the hopper through the

ducts

105, 106, disposed between the shielding member 103 and upper walls of the vessel 100.

Uniformity of the radiation dose applied to the material over the cross section of the vessel may also be obtained by each knife cylinder being associated with a motor (not shown) whose rotational speed is adapted to the radiation intensity of that zone of the grid which extends over the knife cylinder. The rotational speed of the respective motors would be reduced towards the walls extending in parallel to the knife cylinders where the radiation intensity is less. The discharge of material at that position will therefore also be less than in the central zone of the vessel cross section and the radiation dose will once again be uniform.

It is also possible, if the rotational speed of all knife cylinders is identical, to reduce the radial length of the knives of the knife cylinders towards the vessel wall so that the discharge in these peripheral zones is once again smaller than in the central zone.

Referring to FIG. 7, the grid can be constructed so as to be supported in a bend resistant manner. To this end, each tube 110 is of rectangular cross section and the irradiation elements lllll disposed therein are accordingly constructed of flat, rectangular cross section 112. In addition, two sheet metal webs 113 connect each tube 110 to a rod 114 so that together they form a supporting member 115 which is resistant to bending. Owing to the small height h of the irradiation elements 111, the self-absorption of radiation in the direction of the height h is small and the intensity of the radiation discharged in this direction, that is, in the direction of the longitudinal axis of the vessel, is large.

The invention thus provides an irradiation system which has a very high irradiation efficiency due to the absence of absorbing intermediate walls. Since such walls are eliminated, the entire construction of the system is simple and the use of expensive, non-corrosive material is reduced to a minimum. Also, since the material requires only a uniform flow rate, adjustment and stabilization of the rate can be simply performed by regulating the supply and delivery of the material.

The invention further provides an irradiation system in which the processed material is only slightly mechanically stressed.

What is claimed is:

1. Radioactive irradiation apparatus including a flow vessel having walls for directing a flow of material therethrough; feeding means for supplying the material into said vessel; and a discharge means extending over the entire cross-section of said vessel for obtaining a constant rate of flow through said vessel; and a grid of spaced parallel tubes containing irradiation elements, said grid extending at right angles to the flow path of the material to be irradiated over the entire cross-section of said vessel for emitting radiation upstream and/or downstream of said grid, at least one of said tubes and said elements being oriented in said grid with a closer relative spacing near said walls of said vessel than in the central region of said vessel whereby said grid is adapted to meet varying radiation conditions prevailing over the cross-section of said vessel to obtain a nearly uniform radiation dosage in the material to be irradiated flowing through said vessel.

2. An irradiation system as set forth in claim 1 wherein said tubes and elements adjacent to the walls of said vessel parallel to said tubes and elements are more closely spaced apart than said tubes and elements in the center zone of said grid relative to said walls.

3. An irradiation system as set forth in claim 1 wherein said tubes and elements adjacent to the walls of said vessel perpendicular to said tubes and elements are more closely spaced apart than said tubes and elements in the center zone of said grid relative to said walls.

4. An irradiation system as set forth in claim 1 wherein said discharge means includes a plurality of part discharge means for regulating the discharge of material therethrough in relation to the irradiation and flow resistance conditions of the material.

5. An irradiation system as set forth in claim 4 wherein each part discharge means includes a hopper and a rotatably mounted knife cylinder in a discharge zone of said hopper, said cylinder having a plurality of knives extending approximately radially over the length of said cylinder to form pockets therebetween.

6. An irradiation system as set forth in claim 5 which further comprises displacement members in respective ones of said pockets, said displacement members having cross sectional dimensions which increase towards the walls of said vessel extending perpendicularly of said knife cylinder.

7. An irradiation system as set forth in claim 5 wherein each said cylinder is of increased diameter than an adjacent cylinder relative to the walls of said vessel parallel to said cylinders.

8. An irradiation system as set forth in claim 5 wherein the distance between each said knife cylinder and an adjacent cylinder in the central zone of said vessel is smaller than the distance between the knife cylinders adjacent the walls of said vessels.

9. An irradiation system as set forth in claim 5 further comprising a motor connected to each knife cylinder, whereby the rotational speed of each motor can be adapted to the radiation intensity of the grid zone about the respective knife cylinder.

10. An irradiation system as set forth in claim 5 wherein the cross sectional area of each said pocket decreases towards the respective ends of said knife cylinder.

11. An irradiation system as set forth in claim 1 wherein said feeding means includes a storage hopper upstream of said vessel having a discharge opening and a radiation shielding member for substantially preventing the material in said hopper from being exposed to irradiation from said vessel.

12. An irradiation system for granular material comprising a flow vessel for directing a flow of material therethrough;

a plurality of irradiation members disposed in said vessel in a pattern perpendicularly to the flow direction of the material and extending over the cross section of said vessel, the irradiation pattern of said members being oriented in at least one direction of an upstream direction and a downstream direction; and

means for obtaining a substantially constant flow of material through said vessel, said means including a feeding means for introducing granular material into said vessel and a discharge means for removwherein said discharge means includes a plurality of part discharge means for regulating the discharge of material therethrough in relation to the irradiation and flow resistance conditions of the material.

l l l

Claims

12. An irradiation system for granular material comprising a flow vessel for directing a flow of material therethrough; a plurality of irradiation members disposed in said vessel in a pattern perpendicularly to the flow direction of the material and extending over the cross section of said vessel, the irradiation pattern of said members being oriented in at least one direction of an upstream direction and a downstream direction; and means for obtaining a substantially constant flow of material through said vessel, said means including a feeding means for introducing granular material into said vessel and a discharge means for removing said irradiated material from said vessel at different rates across the cross-section of said vessel commensurate with the irradiation and flow resistance conditions of the material to obtain a substantially uniform radiation dosage in the material.

13. An irradiation system as set forth in claim 12 wherein said discharge means includes a plurality of part discharge means for regulating the discharge of material therethrough in relation to the irradiation and flow resistance conditions of the material.