Controlling bulk particulate flow rates

Abstract

A method of transferring particulates from a storage silo to another container or to a process, in which the particulates are fed from the silo into a transfer device comprising a conduit having a first convergent section ( 2 ) converging in the direction of particulate flow followed by a second convergent section ( 3 ) also converging in the direction of particulate flow. The convergence geometry is arranged so that the particulates passing though the conduit under gravity are discharged from the outlet of the second convergent section in a vena contracta flow pattern. The vena contracta effect provides a structured outlet flow where a portion of the outlet flow is narrower than the outlet itself and this enables high flow rate filling of vessels or containers through relatively small apertures (e.g. tanker hatches).

1 . A method of transferring particulates from a storage silo to another container or to a process, in which the particulates are fed from the silo into a transfer device comprising a conduit having a first convergent section converging in the direction of particulate flow followed by a second convergent section converging in the direction of particulate flow, and the convergence of the second convergent section or the first and second convergent sections is arranged so that the particulates passing though the conduit under gravity are discharged from the second convergent section in a vena contracta flow pattern. 
     
     
         2 . A method according to  claim 1  in which air is injected into the second convergent section in a controlled amount that assists formation of the vena contracta. 
     
     
         3 . A method according to  claim 1  in which the first convergent section includes first and second pairs of opposed wall surfaces which connect with respective first and second pairs of opposed wall surfaces of the second convergent section, and in the first convergent section the first pair of opposed wall surfaces converge towards each other in the direction of flow, the second pair being convergent, parallel or divergent, whereas in the second convergent section the second pair of opposed wall surfaces converge towards each other in the direction of flow, the first pair being convergent, parallel or divergent. 
     
     
         4 . A method according to  claim 1  in which the first convergent section includes at least two opposed wall surfaces which converge towards each other in the direction of flow to form a slot outlet at the junction between the first convergent section and the second convergent section, and the second convergent section includes at least two opposed wall surfaces which converge towards each other in the direction of flow to form a slot outlet for discharge of particulates, the two slot outlets extending in respective directions that are substantially normal to each other. 
     
     
         5 . A method according to  claim 3 , in which the first convergent section of the conduit converges to form a slot outlet at the junction between the first convergent section and the second convergent section, and the second convergent section converges to form a slot outlet for discharge of particulates, the two slot outlets extending in respective directions that are substantially normal to each other. 
     
     
         6 . A method according to  claim 1  in which the conduit includes an inlet section upstream of the first convergent section. 
     
     
         7 . A method according to  claim 6  in which the inlet section has parallel walls. 
     
     
         8 . A method according to  claim 1  in which the conduit includes a non-convergent section between the first convergent section and the second convergent section. 
     
     
         9 . A method according to  claim 1  in which the geometry of the second convergent section is arranged so that the flow discharge of the intended particulates takes the form of a vena contracta. 
     
     
         10 . Device for gravity transfer of bulk particulates comprising an open-ended conduit having a first convergent section and a second convergent section, in which in use particulates pass from the first convergent section to the second convergent section, the first convergent section including first and second pairs of opposed wall surfaces which connect with respective first and second pairs of opposed wall surfaces of the second convergent section, and in the first convergent section the first pair of opposed wall surfaces of the first convergent section converge towards each other in the direction of flow, the second pair being convergent, parallel or divergent, whereas in the second convergent section the second pair of opposed wall surfaces of the second convergent section converge towards each other in the direction of flow, the first pair being convergent, parallel or divergent, in which the convergence of the second section or the first and second sections is arranged so that in use particulates are discharged in a vena contracta flow pattern. 
     
     
         11 . Device according to  claim 10 , in which the first convergent section of the conduit converges to form a slot outlet at the junction between the first convergent section and the second convergent section, and the second convergent section converges to form a slot outlet for discharge of particulates from the second convergent section, the two slot outlets extending in respective directions that are substantially normal to each other. 
     
     
         12 . Device for gravity transfer of bulk particulates comprising an open-ended conduit having a first convergent section and a second convergent section, in which in use particulates pass from the inlet section to the second convergent section, in which in the first convergent section at least two opposed wall surfaces converge towards each other in the direction of flow to form a slot outlet at the junction between the first convergent section and the second convergent section, and in the second convergent section at least two opposed wall surfaces converge towards each other in the direction of flow to form a slot outlet for discharge of particulates from the second convergent section, the two slot outlets extending in respective directions that are substantially normal to each other, and in which the convergence of the second section or the first and second sections is arranged so that in use particulates are discharged in a vena contracta flow pattern. 
     
     
         13 . Device according to  claim 10  in which the first convergent section has first and second pairs of opposed wall surfaces which connect with respective first and second pairs of opposed wall surfaces of the second convergent section, and in the first convergent section the first pair of opposed wall surfaces of the first convergent section converge towards each other in the direction of flow and the second pair are substantially parallel, and in the second convergent section the second pair of opposed wall surfaces of the second convergent section converge towards each other in the direction of flow and the first pair are parallel. 
     
     
         14 . Device according to  claim 10  in which the area of the outlet of the second convergent section is from 20-80% of the area of the inlet of the second convergent section. 
     
     
         15 . Device according to  claim 10  including means for injecting air into the conduit. 
     
     
         16 . Device according to  claim 10  in which the conduit includes an inlet section upstream of the first convergent section. 
     
     
         17 . Device according to  claim 16  in which the walls of the inlet section are parallel. 
     
     
         18 . Device according to  claim 10  in which the conduit includes a non-convergent section between the first convergent section and the second convergent section. 
     
     
         19 . Device according to  claim 11  in which the first convergent section has first and second pairs of opposed wall surfaces which connect with respective first and second pairs of opposed wall surfaces of the second convergent section, and in the first convergent section the first pair of opposed wall surfaces of the first convergent section converge towards each other in the direction of flow and the second pair are substantially parallel, and in the second convergent section the second pair of opposed wall surfaces of the second convergent section converge towards each other in the direction of flow and the first pair are parallel. 
     
     
         20 . Device according to  claim 12  in which the first convergent section has first and second pairs of opposed wall surfaces which connect with respective first and second pairs of opposed wall surfaces of the second convergent section, and in the first convergent section the first pair of opposed wall surfaces of the first convergent section converge towards each other in the direction of flow and the second pair are substantially parallel, and in the second convergent section the second pair of opposed wall surfaces of the second convergent section converge towards each other in the direction of flow and the first pair are parallel.