Abstract:
Fluidizing transport apparatus comprises a hopper, a pressure vessel and a valve element which controls a port between the hopper and the vessel. The valve element is retained closed against the port under pressure within the vessel. A fluidizing nozzle receives transport fluid, such as water from a fluid line. Water supplied through the fluid line thus fluidizes solids in the vessel and raises the pressure to maintain the valve element in the closed position. The fluidized solids material is then supplied to a transport pipeline from the vessel. Solids material loaded into the hopper depress the valve element when pressure within the vessel is relieved, so allowing a fresh charge of the solids material to enter the vessel for a subsequent cycle. The position of the valve element within the vessel is influenced by a float which responds to the water level within the hopper.

Description:
FIELD OF INVENTION 
       [0001]    The present invention relates to apparatus for transporting a particulate material. 
       BACKGROUND TO THE INVENTION 
       [0002]    Hydro-transport, or the transport of particulate materials in slurry form, usually entrained in a flow of water, is used in the mining and mineral industries. The material is fluidized in batches and conveyed along pipelines. Such processes can be used in many other industries where solids are moved, such as filtration, water softening, catalyst regeneration and grit or shot blasting systems. 
         [0003]    Fluidizing transport systems in which the material to be transported is fluidized in a pressure vessel and then discharged from the vessel under fluid pressure are disclosed in U.S. Pat. No. 4,978,251, U.S. Pat. No. 4,952,099, U.S. Pat. No. 5,853,266 and WO2007015091. Such systems are capable of transporting slurries from the pressure vessel at much higher solids concentrations than a traditional slurry pump, are more energy efficient, and have the advantage that no moving parts come into contact with the solids. 
         [0004]    The problem with these fluidizing systems is that, owing to the high concentrations of solids and the speed of transfer of the solids from the pressure vessel into the transport pipeline, the vessel must be replenished with solids rapidly to keep up with the discharge. This requires the vessel to be depressurized and solids loaded, normally under gravity, into the top of the vessel. In order to load quickly, the pressure vessel has a fill valve or port which is generally a minimum 4 times larger than the discharge pipe. The valve must be quick-acting, pressure-retaining and solids tolerant, and be capable of undergoing several hundred thousand operating cycles. Valves on large-scale systems may be 1 meter diameter or greater. 
         [0005]    The above constraints are generally beyond the normal operating limits of many valves. A valve capable of this duty is generally large and expensive making the use of fluidizing transport systems uneconomical. 
         [0006]    Hard seat ball valves or plug valves can be used, but the operating conditions and abrasive nature of the solids cause rapid wear of valve seats and seals, necessitating a high level of maintenance. 
         [0007]    Owing to the size of the valves, the actuators which drive them are equally large and require frequent maintenance. The plant must be taken out of service during maintenance work, resulting in down time and lost production, together with associated costs. 
         [0008]    Pinch valves are known to be solids tolerant and can be pneumatic or mechanically operated; however, they do not have a high pressure capability, have a limited size, and so are not suitable except on low pressure low volume systems. 
         [0009]    Knife valves, whilst generally smaller in depth, can be used but again require an actuator and have a limited operating pressure. The seals employed in knife valves are generally not suitable for continuous cyclic operation. 
         [0010]    Fluidization hydro-transport systems rely generally on a flooded pressure vessel and a solids accumulation hopper located above, and operate as follows. While the hopper is being loaded with solids, the standing fluid within the hopper is displaced from the hopper via an overflow pipe. When the hopper has been filled with solids, water will be present in the hopper within the voidage of the solids. The transport fluid is usually water. Consequently, it will be referred to as water in this specification but it will be appreciated that other fluids, usually liquids can be used. 
         [0011]    Water as the transport fluid is fed into a fluidizing unit within the pressure vessel, the fluid displacing the solids present in the pressure vessel until all the solids are discharged. This leaves the vessel full of water. 
         [0012]    When the pressure vessel is empty of solids the valve between the hopper and vessel is opened and solids fall by gravity into the pressure vessel. Water within the vessel is displaced by the higher density solids entering the vessel. This results in solids falling through a counter-flow of water rising through the valve opening from the vessel, which can hold up or restrict the loading of solids. 
         [0013]    To overcome this, a separate displacement or bypass line complete with a simple shut-off valve can be provided, extending from the top of the vessel to the top of the hopper. This allows the majority of displaced water to bypass the large solids loading valve. This reduces the counter-flow of water through the valve to allow the solids to fall into the vessel unhindered which speeds up the loading time. In all cases the hopper and vessel are in a flooded state either before or after loading. 
         [0014]    Once the vessel is loaded, the valves around the vessel are closed, and feed to the fluidizing head is opened. This feeds water into the vessel via the fluidizing head and brings the vessel up to working pressure, normally within 1 or 2 seconds. The solids then discharge as slurry into a transport pipeline. 
       SUMMARY OF INVENTION 
       [0015]    According to the present invention there is provided apparatus for transporting a particulate material, the apparatus comprising a vessel and a hopper for the particulate material, the hopper being situated above the vessel and communicating with the vessel at a port which is closeable by a valve element, the vessel having a liquid feed inlet for admitting liquid under pressure into the vessel, and an outlet for discharging a fluidized mixture of the liquid and the particulate material, the valve element being provided with a floatation device which biases the valve element upwards in the liquid, the floatation device being provided in the hopper and being connected to the valve element by a connecting element which extends through the port. 
         [0016]    According to another aspect of the present invention there is provided a method of transporting a particulate material comprising:
       (a) delivering the particulate material to a hopper which communicates through a port with a vessel situated below the hopper and containing a transport fluid, the port being closed by a valve element, which is buoyant by virtue of a float disposed in the hopper and connected to the valve element, whereby the position of the valve element is influenced by the level of fluid in the hopper;   (b) allowing the valve element to move under the weight of particulate material in the hopper to open the port, whereby the particulate material falls through the port into the vessel;   (c) admitting further transport fluid into the vessel thereby pressurizing the transport material and causing the valve element to move to close the port;   (d) opening a transport valve to allow fluid within the vessel to flow to a pipeline; and   (e) fluidizing the particulate material in the transport fluid whereby the particulate material is entrained in the transport fluid delivered to the pipeline.       
 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0022]    For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a diagrammatic view showing fluidizing transport apparatus; 
           [0024]      FIG. 2  corresponds to  FIG. 1  but shows the apparatus in a different operating condition; 
           [0025]      FIG. 3  diagrammatically shows two fluidizing units operable in the same fluidized transport; 
           [0026]      FIG. 4  is a plan view of one connection arrangement for apparatus as shown in  FIG. 3 ; 
           [0027]      FIG. 5  corresponds to  FIG. 4  but shows an alternative connection arrangement; 
           [0028]      FIG. 6  corresponds to  FIGS. 4 and 5  but shows a third embodiment of connection arrangement; 
           [0029]      FIG. 7  corresponds to  FIG. 1  but shows a modified form of fluidizing transport apparatus; 
           [0030]      FIG. 8  corresponds to  FIG. 7 , but shows another modified fluidizing transport apparatus; 
           [0031]      FIG. 9  is an enlarged view of an alternative embodiment of valve suitable for use in a fluidizing transport apparatus as shown in  FIG. 1 ; 
           [0032]      FIG. 10  corresponds to  FIG. 1  but shows another embodiment of fluidizing transport apparatus; and 
           [0033]      FIG. 11  is an enlarged view of a valve in the apparatus of  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    Referring to  FIGS. 1 and 2 , the apparatus comprises a hopper  2  for receiving a solid material, such as sand or other particulate material. The hopper may be loaded with the solid material by conventional means, such as a screw conveyer (not shown). Beneath the hopper  2  there is a pressure vessel  4 . The hopper  2  communicates with the pressure vessel  4  through a port  6 . The port may be closed by a valve element  8  which is mounted on a connecting rod  10  which extends through the port  6  and is provided with a flotation device in the form of a closed spherical float  12 . 
         [0035]    A fluidizer nozzle  14  is situated within the vessel  4 , towards it lower end, and is connected to a fluid feed inlet  16  by a shut-off valve  18 . 
         [0036]    A slurry outlet  20  is provided generally at the same level as the feed inlet  16 , i.e. towards the lower region of the vessel  4  and is connected by an outlet shut-off valve  22  to a transport pipeline  24 . 
         [0037]    A bypass or displacement line  26 , provided with a bypass shut-off valve  28 , extends from the upper region of the vessel  4  to discharge into the top of the hopper  2 . 
         [0038]    The hopper  2  is provide at its upper region with an overflow outlet  30 . 
         [0039]    In the conditions shown in  FIG. 1 , the vessel  4  contains a load of the solid material  32 , the remainder of the vessel  4  being filled with a transport fluid which, in all of the embodiments described with reference to the Figures, is water. 
         [0040]    The valve  8  is shown closed, being biased upwardly by a float  12  which floats in a body of water contained in the hopper  2 . The level  34  is temporarily above the level of the overflow  30 , because the hopper  2  has received water from the vessel  4 , through the bypass line  26 , displaced by the incoming solids  32 . 
         [0041]    When the apparatus reaches the condition shown in  FIG. 1 , the bypass valve  28  is closed, and the inlet valve  18  and the outlet valve  22  are opened. This causes the pressure within the vessel  4  to rise, maintaining the valve  8  in the closed position. Thus, even though the water level  34  in the hopper  2  will fall as excess water drains through the overflow outlet  30 , the pressure in the vessel  4  is sufficient to maintain the valve element  8  closed against the port  6 . 
         [0042]    Incoming flow through the feed  16  is delivered to the fluidizing nozzle  14  and also through a balance pipe  36  to a position near the top of the vessel  4 . The flow through the fluidizing nozzle  14  fluidizes the particulate solids material  32 , and the fluidized material, in the form of a slurry, is discharged through the slurry outlet  20  to the transport pipeline  24 . This operation continues until all of the solids material in the vessel  4  has been discharged. While the discharge is occurring, the next batch of the solids material is loaded into the hopper  2 . 
         [0043]    When discharge of the solids material  32  is complete, the inlet valve  18  and the outlet valve  22  are closed and the bypass valve  28  is opened. Pressure in the vessel  4  is thus relieved through the bypass line  26 , reducing the upwards pressure acting on the valve element  8 . The weight of the solids material loaded into the hopper  2  is greater than that of water, and consequently this weight, acting on the valve element  8  is sufficient to move the valve element  8  downwardly, as shown in  FIG. 2 , allowing the solids  32  to fall from the hopper  2  into the pressure vessel  4 . As mentioned above, this causes water to be displaced from the vessel  4  through the bypass line  26  into the hopper  2 , replacing the departing solids material. The connecting rod  10  extends through the valve element  8  to form a guide rod  38  which cooperates with a guide element  40 , secured to the wall of the vessel  4 , to maintain the central positioning of the valve element  8 . As the solids material  32  falls through the port  6 , it acts on the valve element  8  to displace it lower in the vessel  4 . Also, in the transient state as water is displaced from the vessel  4  through the bypass line  26  to the hopper  2 , the water level  34  drops below the level of the overflow outlet  30  and this contributes to lowering of the valve element  8  and increased opening of the port  4 . 
         [0044]    In addition, the port  6  has a diameter larger than that of the slurry outlet  20 , for example at least four times the diameter. Consequently, the transfer of the solids material  32  from the hopper  2  to the vessel  4  takes place rapidly, minimizing the time between the discharge of successive batches of the material  32  to the transport pipeline  24  . 
         [0045]    When the transfer of the material  32  from the hopper  2  to the vessel  4  is complete, the bypass valve  28  is closed and the inlet valve  18  and the outlet valve  22  are opened. As water begins to flow into the vessel  4 , a proportion of it flows through the balance pipe  36 . Consequently, a supply of clean water flows into the region of the valve  8 , and through the port  6  in the upward direction, so scouring any remaining solids material from the upper surface of the valve element  8 . This flow, along with the displacement flow through the bypass line  26 , raises the level  34  in the hopper  2  as mentioned above. The float  12  therefore rises to move the valve element towards the port  6 , assisted by the pressure differential across the port  6  caused by the incoming flow into the vessel  4 . The port  6  is thus closed by the valve element  8 , and the process repeats in the manner described above with reference to  FIG. 1 . 
         [0046]    It would be appreciated that, if a single fluidizing unit is provided, comprising the hopper  2  and the vessel  4 , the delivery of fluidized slurry to the transport pipeline  24  will take place in a batch like manner. In one embodiment, therefore, a pair of the fluidizing units is provided, as diagrammatically represented in  FIG. 3 . In this arrangement, a connecting manifold  42  is provided which comprises a common outlet  44  connected to the transport pipeline  24  (not shown). The manifold  42  has a pair of inlet sections  46 ,  48 , connected respectively to the slurry outlets  20  of two vessels, vessel A and vessel B. 
         [0047]    The fluidizing units represented by vessel A and vessel B in  FIG. 3  are identical to that shown in  1  and  2  and so will not be described again in detail. However, in operation of the apparatus as shown in  FIG. 3 , it will be appreciated that, while vessel A is receiving solids material  32  from the hopper  2  through the open valve element  8 , the pressure vessel  4  of vessel B is receiving water through the inlet fluid line  16  to discharge the solids material  32  through the slurry outlet  20 , the respective inlet section  48 , and the outlet  44 . 
         [0048]    In  FIGS. 1 to 3 , the float  12  is shown fixed on the upper end of the connecting rod  10 . As an alternative, it is possible for the float  12  to be mounted displaceably on the connecting rod  10 , so that its position relative to the valve element  8  can be adjusted. This adjustment enables the position of the valve element  8  to the port  6  to be varied, to provide an optimum operating characteristic in terms of the maximum opening position of the valve element  8  to allow rapid discharge of material from the hopper  2  to the vessel  4 , and the time taken for the valve element to close against the port  6  when water entering the vessel  4  through the feed line  16  raises the pressure within the vessel  4 . 
         [0049]    Although not shown in  FIG. 3  a non-return valve arrangement is required in the manifold  42  to prevent backflow of slurry from the discharging vessel  4  to the other loading vessel  4 .  FIGS. 4 to 6  to show various valve arrangements which can be used. 
         [0050]    In  FIG. 4 , all check valves  50  are employed in the inlet sections,  46 ,  48 . The valves  50  are oriented so that the valve wall  52  is biased by gravity to a position in which it closes the inlet section  46 ,  48 . Thus, the slurry flow from the vessel  4  which is discharging (vessel B) in the slurry flow from the vessel  4  which is discharging (vessel B in the conditions shown in  FIG. 4 ) causes the ball  52  to be displaced out of the fluid path, allowing the slurry to pass to the outlet  44 . Since the interior of the loading vessel  4  (vessel A in the condition shown in  FIG. 4 ) is atmospheric, and consequently the elevated pressure in the inlet section  46  presses the ball  52  against its seat, preventing slurry from vessel B from returning through the inlet section  46  to the vessel A. 
         [0051]      FIG. 5  shows an alternative embodiment in which the ball valves  50  are replaced by pinch valves  54 . In this embodiment, control means are required to open and close the pinch valves  54  at the appropriate times. In the conditions shown in  FIG. 5 , vessel B is discharging, and the respective pinch valve  54  is open, while vessel A is loading, and the respective pinch valve  54  is closed to prevent back-flow in into it. Whereas the ball valves of  FIG. 4  can be used in high-pressure systems, and do not require positive activation, the pinch valves  54  of  FIG. 5  are suitable for only relatively low-pressure systems and require actuators, for example, hydraulic, pneumatic or mechanical actuators, controlled by a suitable control arrangement. 
         [0052]      FIG. 6  shows a single ball diverter valve  56 , comprising a ball  58  which is mounted for pivotable displacement between the outlet ends of the respective inlet sections,  46 ,  48 . In the conditions shown in  FIG. 6 , as in  FIGS. 4 and 5 , vessel B is discharging, while vessel A is loading. The ball  58  is thus swung, by the flow from vessel B, over the outlet end of the inlet section  46  vessel A. Consequently, backflow to the vessel A is prevented. Such diverter valves can be used in high-pressure systems and do not require actuators or associated control arrangements. 
         [0053]      FIG. 7  shows a variant of the apparatus as shown in  FIGS. 1 and 2 . It would be appreciated that, in the embodiment of  FIGS. 1 and 2 , solids material being loaded into the hopper  2  may strike the float  12 . This may damage the float  12  or depress it into the water within the hopper  2  so displacing the valve element  8  away from the port  6 . In order to avoid this, a shield  60  may be supported within the hopper  2  enclosing and protecting the float  12 . The shield  60  is preferably provided with a vent hole so that the water level within the shield  60  rises and falls with the water level  34  outside the shield  60 . Thus, operation of float  12  is not affected, shroud  60  protects it from solids material falling into the hopper  2 . 
         [0054]      FIG. 8  shows an alternative arrangement for controlling the position of the valve element  8 . Instead of the float  12 , the variant shown in  FIG. 8  employs a hydraulic ram  62 . The ram  62  is supplied with water under pressure through a line  64 , extending from the inlet feed line  16  at a position upstream of the inlet valve  18 . The water under pressure is directed to the respective ends of the ram  62  by control valves  66 ,  68 . Thus, to close the valve element  8  against the port  6  water is supplied through the line  66  through the open valve  68  to raise the connecting rod  10 , taking with it the valve element  8 . To open the valve element  8 , the control valve  68  is closed and control valve  68  is opened, so that water is admitted to the upper region of the ram  62 , so lowering the valve element  8 . The control valves  66  and  68  may be controlled manually by an operator, or may be controlled from an automatic control system for the apparatus as a whole. 
         [0055]    Although the use of water from the inlet feed line  16  to drive the ram  62  provides a convenient arrangement, it is possible for the ram  62  to be replaced by other forms of actuators, for example a pneumatic ram controlled by solenoids or by an electric actuator. 
         [0056]      FIG. 9  shows, on an enlarged scale, an alternative embodiment of the valve element  8  and its control arrangement. The valve element  8 , as shown in  FIG. 9 , comprises a core  70 , which may be fabricated or forged from steel, which is provided with a sealing cap  72  which may be formed from an elastomeric material, such as natural rubber or polyurethane which is secured to the core  70 , for example by bonding or molding in situ. Although this construction is described with specific reference to the embodiment of  FIG. 9 , it will be appreciated that the valve element  8  of the preceding embodiments may also be constructed in the same manner. 
         [0057]    The cap  72  cooperates with a valve seat  74  which defines the port  6 . The valve element  8  is connected by the connecting rod  10  to a floatation device in the form of an inverted bucket  76 . The connecting rod  10  is screw threaded, at least at its upper end, and the bucket  76  is adjustably connected to the connecting rod  10  by adjustment nuts  78 . The bucket  76  is provided with an air control valve  80  through which air can be admitted or withdrawn from the interior of the bucket  76  to adjust the position of an internal water level  82 . 
         [0058]    The core  70  of the valve element  8  defines an internal chamber  84 . The core  70  may, like the bucket  76 , have an air control valve similar to the valve  80 , but not shown in  FIG. 9 . This additional air control valve enables air to be supplied to, or withdrawn from the chamber  84  to adjust the internal water level  86 . 
         [0059]    In general, the valve arrangement shown in  FIG. 9  operates in a similar manner to that of  FIGS. 1 and 2 . However, it will be appreciated that the buoyancy of the valve assembly, comprising the valve element  8  and the bucket  76 , can be adjusted by introducing air to the bucket  76  and/or the chamber  84 . This enables the behavior of the valve element  8  in operation to be adjusted to achieve desired characteristics. For example, increasing the volume of air within the bucket  76  and the chamber  84  will increase the buoyancy of the assembly, so as to decrease the time taken for the valve element  8  to move from the open position to the closed position. 
         [0060]    It will be appreciated that such adjustment can be achieved using only the bucket  76  or only the chamber  84 . It is envisaged that the chamber  84  will not be required where the valve element  8  is relatively light, although the additional buoyancy which is provided may be beneficial where the valve element has a relatively large mass. 
         [0061]      FIGS. 10 and 11  show an embodiment similar to that of  FIG. 9 , although the bucket  76 , and the connecting rod  10 , are omitted. Thus, the valve element  8 , as before, comprises a core  70  and a cap  72 , but the buoyancy of the valve assembly is achieved by the chamber  84  alone. Again, an air control valve (not shown) is provided to enable air to be introduced into, or withdrawn from, the chamber  84  to adjust the internal water level  86 . In the embodiment of  FIGS. 10 and 11 , the guide element  40  is provided with an upstanding guide tube  38  to ensure adequate guidance of the valve element  8  in the absence of the stabilizing effect provided by the float  12  or the bucket  76 . 
         [0062]    As shown in  FIG. 11 , the core  70  is generally cup-shaped and the cap  72  is in the form of a relatively thin layer of elastomeric or other yielding material which is bonded to the core  70 . The profile of the core  70  and consequently of the cap  72  is configured to provide an upstanding peak  88  in the centre of the valve element  8 , with the remainder of the upper surface of the cap  72  having a smoothly curving profile to the radially outer edge of the valve element  8 . This profile assists in avoiding the accumulation of the solid material on the valve element  8 . Instead, the flow of water through the port  6 , once all solids have been discharged from the hopper  2 , scours any deposited solid material from the valve element  8 . Removal of such solid material is also assisted by the counter flow of water from the vessel  4  during the solids filling process, and the flow of incoming water through the balance pipe  36 . 
         [0063]    Preferably, the quantity of air within the chamber  84  (or within the chamber  84  and the bucket  76  when provided), is such that the entire valve assembly is approximately neutrally buoyant in the water within the vessel  4  and the hopper  2  (or other transport liquid, if used). In a specific example, it has been found that, for a valve assembly (i.e. the valve element  8 , the guide rod  38  and any other components attached to the valve element  8 ) having a total mass of 1.25 kg, the volume of air required in the chamber  84  to achieve neutral buoyancy is 1.4 liters.