A DEVICE AND A METHOD FOR WEIGHING A MATERIAL THAT IS SUPPLIED TO A CONTAINER, DURING PROCESSING THEREOF

Abstract: A device for weighing a material that is supplied to a container (1) during processing thereof presents a processing member (3) for processing the material, which processing member is driven by an outer driving member (4, 7) and arranged in the container (1). The driving member (4, 7) is connected to the processing member (3) by a connection (8) which, at least during operation, transmits axial forces. The processing member (3), in co-operation with the supplied material, gives rise to dynamic forces acting between the included components. The device presents a first weighing member (26) which is mechanically connected to the container (1) and arranged to determine a weight associated to the container. Furthermore, the device comprises a second weighing member (27) which is mechanically connected to the driving member (4, 7) and arranged to determine the weight associated to the driving member. With consideration taken to the weights determined by the first and second weighing members (26, 27), the weight of the supplied material is calculated in an evaluating member.

Description: A device and a method for weighing a material that is supplied to a container, during processing thereof THE FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a device for weighing a material supplied to a container during processing thereof, which device presents a processing member for processing material, which processing member is driven by an outer driving member and arranged in the container, the driving member being connected to the processing member by means of a connection which, at least during operation, transmits axial forces, and the processing member, in co-operation with the supplied material, giving rise to dynamic forces acting between the included components. The invention also relates to a method for weighing a material .that is supplied to a container during processing thereof, which container presents a processing member for processing the material, said processing member being driven by an outer driving member and arranged in the container, said driving member being connected to the processing member by means of a connection which, at least during operation, transmits axial forces, and the processing member, in co-operation with the supplied material, giving rise to dynamic forces acting between the included components. Some of the waste received from nuclear power plants, for instance ion exchanger mass or salt solutions, are permanently stored as cast in concrete. To accomplish this, it is known to form a water solution or a water suspension with radioactive waste, which solution or suspension is mixed with cement powder in a mixing vessel by means of an agitator which presents a vertical rotation axis which coincides with the central line of the vessel and which is supported at the bottom of the vessel. The agitator may form a so called "lost" agitator, which is left in the vessel after termination of the mixing. During the course of the mixing the ingredients of the mixing recipe are successively added, the added amount being supervised by means of a balance which is located below and weighs the total mixing vessel. Weight limit values obtained are used to control the amount of each ingredient respectively of the recipe. The agitator is driven by a driving device with a rotating vertical pivot pin which is in engagement with the upper shaft end of the agitator. During the mixing axial position changes of vessel and agitator occurs depending on dynamic forces, increasing loads, thermic expansion etc. These position changes are transformed into vertical forces which act upon the balance due to the connection between the driving pin and the agitator being subjected to friction. The disturbances of the weight measurement thus created make an accurate dosing by use of weight limit values impossible. FR-A-2 422 232 shows a container for terminal storage of radioactive waste, which is supplied to the container together with, for instance, cement, the supplied material being mixed by means of a "lost" agitator. SUMMARY OF THE INVENTION The object of the present invention is to improve the possibilities of weighing a material which is supplied to a container while, simultaneously, the supplied material is processed. This object is obtained by the device initially defined, which is characterized by a first weighing member which is mechanically connected to the container and arranged to determine the weight associated to the container, a second weighing member which is mechanically connected to the driving member and arranged to determine the weight associated to the driving member, and an evaluating member which is arranged, with consideration taken to the weights determined by the first and second weighing members, to calculate the weight of the supplied material. By taking into consideration the weight of the driving member, on one hand, and the container, on the other hand, it is possible to eliminate the disturbances which arise during the processing. The forces acting between the driving member and the processing member will give rise to identical loads on both the weighing members, but with reversed signatures. By summing the two signals of the weighing members, these disturbances will cancel each other out. It is of importance to be able to correctly define the weight and, thus, the amount of the ingredients supplied to obtain an accurate proportion between these ingredients. It is also of importance for obtaining the accurate total amount in the container; during terminal storage of radioactive waste, it is desirable to fill the containers all the way up, so that no empty spaces are created, something that would steal space and decrease the strength of the containers. According to one embodiment the evaluating member is connected to the first and the second weighing members and arranged to determine the weight of the supplied material as the difference between the sum of the weighing results of the first and the second weighing members and the original weight of the container, the processing member and the driving member. According to another embodiment, the evaluating member may comprise a first evaluating unit which is connected to the first weighing member and arranged to calculate the weights associated to the container, and a second evaluating unit which is connected to the second weighing member and arranged to calculate the weight associated to the driving member, and a calculating unit which is connected to the two evaluating units and arranged to determine the weight of the supplied material as the difference between the sum of the weights calculated by the first and second evaluating units and the original weight of the container, the processing member and the driving member. By this second embodiment, both the weighing members may be optional, that is they do not need to be identical, but the two weights are calculated respectively and, thereafter, are summed by means of the calculating unit. To be able to determine precisely the weight of the supplied material, the evaluating member should be arranged to calculate the former on the basis of weights simultaneously determined by the first and second weighing members. In other words it is of importance that the first and second weighing members are read simultaneously. Furthermore, it is advantageous that the first and the second weighing members are arranged to determine the instantaneous weight associated to the container and the driving member respectively. According to a further embodiment, each of the first and second weighing members may comprise a group of weighing elements, for instance three as to the number. The weighing elements in the first and second weighing members may, advantageously, be arranged in an circular configuration. Furthermore, every weighing element may present a longitudinal axis which extends tangentially in the circular configuration of the former, and, advantageously, the two circular configurations are concentrical and each weighing element may present the same distance to the centre axis of the circular configurations. Furthermore, the weighing elements may be arranged with the same angular distance to each other. As the weighing elements in this way are mounted geometrically similarly, the weighing elements of each weighing member may compensate for the tangential forces, such as torque, which act upon the driving member and container. According to a further embodiment, the processing member comprises an agitator for mixing the material. Depending on the weight and viscosity of the material different force transmission between the container and the driving member is obtained. By a further embodiment the driving member is supported by a support member, and the container is insertable under the support member. Thereby, the second weighing member may be mounted on the support member, between the latter and the driving member. According to another embodiment, a dosing connection piece is arranged on the support member, such that it extends downwards towards and into an opening at the upper end of the container as the latter is inserted under the support member and the driving member, a small annular gap being formed between the dosing connection piece and the opening. To prevent any effect upon the weighing result from occurring, it is of importance that the dosing connection piece does not touch or bear on the container. At the same time it is important that the annular gap is as small as possible, so that radioactive aerosols will not reach out to the environment in any larger amount. Advantageously, the dosing connection piece may be connected to an exhaust air system, such that an inwards-directed air flow through the annular gap is formed. In that way, the radioactive aerosols will be sucked out by the exhaust air system. The object is also obtained by the method initially defined, which is characterized by the steps of: - determining the original weight of the container, the processing member and the driving member, - supplying the material to the container, - during a first weighing, determining the weight associated to the container by means of a first weighing member, - during a second weighing, determining the weight associated to the driving member by means of a second weighing member, and - calculating the weight of the supplied material as the difference between the sum of the first and the second weighings and the defined original weight. Advantageous embodiments of this method are defined in the claims 18-21. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described more in detail with reference to different embodiments shown in the accompanying drawings. Fig 1 shows a side-view of a device for mixing a material that is supplied to a container. Fig 2 shows a section through a container and a dosing connection piece. Fig 3 shows a view from above of an agitator. Fig 4 shows a bearing member for the agitator. Fig 5 shows a schematic connection of the weighing members. Fig 6 shows an alternative connection of the weighing members. DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS Fig 1 shows a container for terminal storage of radioactive waste. The container 1 may be an ordinary 200-litre barrel. The container 1 is open at the top and closable by means of a connecting part 2. Further, the container comprises a processing member 3, for instance an agitator. The agitating member 3 is driven by means of the driving motor 4 which is mounted on a support member 5 which is held by a steel structure 6 suspended from the ceiling. The driving motor 4 is connected to a gearbox 7, the outgoing shaft of which (not shown ) extends along the vertical line X-X. The outgoing shaft ends in a driving pin 8 which can engage with the agitator 3. Furthermore, a dosing connection piece 9 is mounted on the support member 5, through which connection piece the outgoing shaft extends. A channel 10 which connects the dosing connection piece 9 to a cement doser 11 opens into the dosing connection piece 9. The channel 10 may comprise a feeding device, for instance a screw feeder, for feeding cement from the cement doser 11. Furthermore, an exhaust air channel 12 opens into the dosing connection piece 9. A fan member 13 is arranged onto the exhaust air channel 12, by means of which fan member air may be sucked out from the interior of the dosing connection piece 9. The agitator 3 is rotatably supported in the container 1 on a shaft pin 14 which is shown more in detail in Fig 4. The shaft pin 14 is fixed onto a cross 15 comprised by flat bars and which is placed in the container 1 and rests against the floor of the container 1 upon support feet 16 by means of which the cross 15 can be adjusted in such a way that the direction of the shaft pin 14 becomes exactly vertical. The shaft pin 14 retains the agitator 3 in a vertical position and permits the rotation of the agitator 3 around the axis X-X. The upper end of the shaft pin 14 is slightly conical, whereby the upper end, which functions as an axial bearing for the agitator 3, obtains a bearing surface with small diameter, reducing the risk for chip formation. The agitator 3, see Fig 2 and 3, presents a tube which has a rectangular cross-section and upon which three plane blades of thin sheet are mounted onto relatively short arms in the example shown. These blades give the material present in the container 1 a flow which is directed vertically downwards. At the lower end of the agitator 3 a longer arm is mounted, which arm carries a blade 20 which gives the material a flow that is directed radially outwards, and a blade 21 which gives the material a flow directed upwards at the periphery of the container 1. The arm of the blades 20, 21 is brought right through the hollow agitator 3 and will bear on the shaft pin 14 and, thereby, form the axial bearing of the agitator. As can be seen especially in Fig 2, the connecting part 2 is provided with an opening 22 into which the lower part of the dosing connection piece 9 projects a short distance. The dosing connection piece 9 is arranged to project only so far that an annular gap 23 is formed between the opening 22 and the dosing connection piece 9. The container 1 stands upon a carriage 24 which is provided with wheels 25. The carriage 24, with the container 1 located thereupon, can thus easily be pushed under the driving device 4 and the dosing connection piece 9. The carriage 24 may be rail-connected. When the container 1 is to be made ready for terminal storage, it is initially filled with a suspension or solution of radioactive waste and water. The radioactive waste may be low or intermediate active and, for instance, be formed by used ion exchanger mass. Thereafter, the container located on the carriage 24 is brought to the dosing connection piece 9 and the container 1 is lifted up towards the latter. This lifting movement may take place by lifting the rail onto which the carriage is rolling or by a lifting device (not shown) situated on the carriage 24. As the container 1 is lifted, the agitator 3, which has a rectangular cross-section, will engage with the driving pin 8, which presents a corresponding, rectangular inner cross- section. Thereafter, the motor 4 is started and the agitator 3 begins to rotate. Thereafter, the cement powder is added successively via the cement doser 11, whereby the level in the container 1 rises and the viscosity of the material is changed from a consistency which initially is watery to a consistency which, at the end of the mixing process, is very slow. To accomplish a well-functioning mixing process, it is required that an important part of the flow in the container 1 is vertical. This is accomplished by the agitator 3, the object of which, on one hand, is to accomplish the vertical flow in the container 1 which is favourable for the mixing, and, on the other hand, favour the mixing of the cement powder into the mixture at the viscosity that increases with the level. Furthermore, the agitator 3 should be mountable in the container 1 through an upper opening with limited diameter, and be manufactured out of cheap materials easy to find. The blades 17, 18, 19 of the agitator 3 thus pump the material downwards in the centre of the container 1. At the bottom of the container 1 the material deviates radially outwards and is transferred to a flow which is directed substantially upwards along the wall of the container 1, said flow being accomplished by means of the blade 21 which pumps the material upwards and at the same time balances the hydraulic forces of the blades 17, 18, 19 pumping downwards. At the upper surface of the material another redirection takes place, to a flow that is directed radially inwards. A delimited crossflow from the periphery towards the centre takes place at all levels in the container 1 and contributes to a good mixing effect. The admixture of cement preferably takes place near the shaft of the agitator 3 through the opening 22, and, by high viscosity, an important detail for the function is that the surface of the material is constantly broken by the blade 17 to permit the cement powder to be processed into the material. To accomplish the vertical flow it is required that the blades 17-21 of the agitator 3 work in such a way that, flow-technically, they are not stalled, that is that the flow over the surface of the blades 17-21 is substantially laminar. Furthermore, it is required that most of the blades 17-21 have a small radius of rotation to delimit the torque transferred to the material, which torque otherwise would delimit the mixing effect as, in that way, all the material would be set in rotation. To accomplish an accurate dosing of cement powder and other possible ingredients, the device shown is provided with two weighing members 26 and 27, see Fig 1, 5 and 6. Each weighing member 26, 27 comprises a number of weighing elements 26a, 26b, 26c and 27a, 27b, 27c. The number of weighing elements may for instance be three, four or more for each weighing member 26, 27. It should be noted that in Fig 1 only one weighing element 26a, 27b of each weighing member 26, 27 is shown. The weighing elements 26a, 26b, 26c and 27a, 27b, 27c are, as is indicated in Fig 5 and 6, arranged in a circular configuration. Each such circular configuration is concentrically arranged in relation to the longitudinal, vertical axis X-X, so that each weighing element 26a, 26b, 26c and 27a, 27b, 27c presents the same distance to the axis X-X. The weighing elements 27a, 27b, 27c are mounted at one end 28 thereof onto the upper side of the support member 5. At their other end 29 they are mounted onto a plate 30 which is situated above and on which the driving motor and the gearbox 7 are mounted, so that the outgoing shaft extends downwards through the plate 30. At one end 28 thereof, the weighing elements 26a, 26b, 26c are mounted onto a plate 32 which is situated above and upon which the container 1 is located. Furthermore, the weighing elements 26a, 26b, 26c and 27a, 27b, 27c are arranged with the same angular distance to each other. Each weighing element also presents a longitudinal axis 33 which extends from the end 28 to the end 29 and tangentially in the circular configuration. Furthermore, the different weighing elements 26a, 26b, 26c and 27a, 27b, 27c, advantageously, are all identical. In accordance with Fig 5 the weighing elements 26a, 26b, 26c and 27a, 27b, 27c are connected to a common evaluating unit 34. The latter is arranged in such a way that it sums the weights from all the weighing elements. If the total weight is the same but the load, for instance, is displaced from the weighing element 26a to the weighing element 27c, the load upon 26a will decrease while the load upon 27c increases, so that no difference of total weight occurs. By this embodiment it is essential that the two weighing members 26, 27 and all the weighing elements included therein are identical. By the embodiment according to Fig 6, each weighing member 26 and 27 comprises its own evaluating unit 35 and 36 respectively. These ones evaluate the total instantaneous weight detected by the weighing members 26 and 26 respectively, and these two weights are thereafter summed in a common calculating unit 37. In that way the same final result is obtained as by the embodiment according to Fig 5, but by the latter embodiment according to Fig 6 it is not necessary that the weighing members 26 and 27 are identical. The weighing is done in the following way. Before the water suspension is added, from the evaluating unit 34 or the calculating unit 37 the total original weight of the container 1 and the agitator 3, and the driving motor 4 and the gearbox 7 are obtained via the weighing member 26 and the weighing member 27 respectively. Thereafter, the water suspension with the radioactive waste is added. Thereby, the total weight is increased in correspondence to the weight of the added water suspension. The container 1 is pushed in under the dosing connection piece 9, and the evaluating unit 34 or the calculating unit 37 is reset. Thereafter, the motor 4 is started and the addition of cement begins. As the agitator 3 rotates, a frictional force is created in a vertical direction between the agitator 3 and the driving pin 8. Therefore, a certain part of the deadweight of the agitator 3 and the hydraulic forces will be detected by the weighing member 27, because the bottom of the container 1 has a tendency to be pushed downwards along with the increased supply of cement. Thanks to the two weighing members 26 and 27 this displacement of the weight from one of the weighing members to the other will, however, not result in any difference in the common evaluating unit 34 or the calculating unit 37, because a decreased weight of the container 1 gives rise to a corresponding, increased weight of the driving motor 4 and the gearbox 7 via the agitator 3. Thanks to the geometrically similar arrangement of the different weighing elements 26a, 26b, 26c and 27a, 27b, 27c, possible torques acting on the container 1 and the driving motor 4 and the gearbox 7 will cancel each other out. Not to disturb the weighing result, it is essential that the dosing connection piece 9 does not touch the container 1. Therefore, the gap 23 must have a certain size. To prevent radioactive aerosols from going out through the gap 23, the dosing connection piece is connected to the exhaust air fan 13 which accomplishes an in-flow of air from outside through the gap 23 and up through the dosing connection piece 9 and out through the channel 12.

Claims: Claims 1. A device for weighing a material that is supplied to a container (1) during processing thereof, said container presenting a processing member (3) , driven by an outer driving member (4, 7) and provided in the container, the driving member (4, 7) being connected to the processing member (3) by a connection (8) which, at least during operation, transmits axial forces, and the processing member (3), in co-operation with the supplied material, giving rise to dynamic forces acting between the included components, characterized by a first weighing member (26) which is mechanically connected to the container (1) and arranged to determine the weight associated to the container, and a second weighing member (27) which is mechanically connected to the driving member (4, 7) and arranged to determine the weight associated to the driving member, and an evaluating member (34, 35, 36, 37) which, with consideration taken to the weights determined by the first and second weighing members (26, 27), is arranged to calculate the weight of the supplied material. 2. A device according to claim 1, characterized in that the evaluating member (34) is connected to the first and the second weighing members (26, 27) and arranged to determine the weight of the supplied material as the difference between the sum of the weighing results from the first and second weighing members and the original weight of the container (1) , the processing member (3) and the driving member (4, 7) . 3. A device according to claim 1, characterized in that the evaluating member comprises a first evaluating unit (35) which is connected to the first weighing member (26) to calculate the weight associated to the container (1), a second evaluating unit (36) which is connected to the second weighing member (27) and arranged to calculate the weight associated to the driving member (4, 7), and a calculating unit (37) which is connected to the evaluating units (35, 36) and arranged to determine the weight of the supplied material as the difference between the sum of the weights calculated by the first and second evaluating units (26, 27) and the original weight of the container (1), the processing member (3) and the driving member (4, 7) . 4. A device according to claims 2 or 3, characterized in that the evaluating member (34, 35. 36, 37) is arranged to calculate the weight of the supplied material on the basis of weights simultaneously determined by the first and second weighing members (26, 27) . 5. A device according to any of the preceding claims, characterized in that the first and second weighing members (26, 27) are arranged to determine the instantaneous weight associated to the container (1) and the driving member (4, 7) respectively. 6. A device according to any of the preceding claims, characterized in that each of the first and second weighing members (26, 27) comprises a group of weighing elements (26a, 26b, 26c; 27a, 27b, 27c) , for instance three to the number. 7. A device according to claim 6, characterized in that the weighing elements (26a, 26b, 26c; 27a, 27b, 27c) of the first and second weighing members are arranged in a circular configuration. 8. A device according to claim 7, characterized in that each weighing element (26a, 26b, 26c; 27a, 27b, 27c) presents a longitudinal axis (33) which extends tangentially in the circular configuration. 9. A device according to claim 7 or 8, characterized in that the two circular configurations are concentric and that each weighing element (26a, 26b, 26c; 27a, 27b, 27c) presents the same distance to the centre axis (X-X) of the circular configurations. 10. A device according to claim 8 or 9, characterized in that the weighing elements (26a, 26b, 26c; 27a, 27b, 27c) are arranged with the same angular distance to each other. 11. A device according to any of the preceding claims, characterized in that the driving member (4, 7) is supported by a support member (5, 6) and that the container (1) is insertable under the support member 12. A device according to claim 11, characterized in that the second weighing member (27) is mounted onto the support member (5, 6) between the latter and the driving member (4, 7) . 13. A device according to claim 11 or 12, characterized in that the container (1) is arranged on a carriage (24) which is displaceable to a position under the support member (5, 6) and the driving member (4, 7) . 14. A device according to any of the claims 11-13, characterized in that a dosing connection piece (9) is arranged onto the support member (5,6) such that it extends down towards and into an opening (22) at the upper end of the container (1) as the latter is inserted under the support member (5, 6) and the driving member (4, 7), an annular gap (23) being formed between the dosing connection piece (9) and the opening (22) . 15. A device according to claim 14, characterized in that the dosing connection piece (9) is connected to an exhaust air system (12, 13), such that an inwards-directed air flow through the annular gap (23) is formed. 16. A method for weighing a material supplied to a container during processing thereof, said container presenting a processing member for processing the material, driven by an outer driving member and arranged in the container, the driving member being connected to the processing member by a connection which, at least during operation, transmits axial forces, and the processing member, in co-operation with the supplied material, giving rise to dynamic forces acting between the included components, characterized by the steps of: - determining the original weight of the container, the processing member and the driving member, - supplying the material to the container, - during a first weighing, determining the weight associated to the container by means of a first weighing member, - during a second weighing, determining the weight associated to the driving member by means of a second weighing member, and - calculating the weight of the supplied material as the difference between the sum of the first and the second weighings and the defined original weight. 17. A method according to claim 16, characterized in that the first and the second weighings take place simultaneously. 18. A method according to claim 16 or 17, characterized in that, by the first and second weighings, the instantaneous weight associated to the container and the driving member respectively is determined. 19. A method according to any of the claims 16-18, characterized in that another material has been supplied to the container and that the materials are processed by means of stirring such that they are mixed. 20. A method according to claim 19, characterized in that the materials comprise cement and radioactive waste in a water suspension or solution.

Inventors: SALOMON HEINZ, SALOMON, HEINZ
Applicants: ASEA ATOM AB, SALOMON HEINZ, ABB ATOM AB, SALOMON, HEINZ
Application year: 1996
Main classification: G01G13
IPC codes: G01G13, G01G15, G21F9