WO1991004932A1 - Materials handling apparatus and method - Google Patents

Abstract

A materials handling apparatus and method wherein materials are pneumatically conveyed along a materials supply pipe (30) having pressure vessels (32, 432) spaced therealong, each pressure vessel including control means (126) adapted alternately to permit and prevent the discharge of retained material from the pressure vessel to a user point. Each materials charge is sufficient to top up all the pressure vessels; discharge of materials is prevented whilst materials are being transported along the materials supply pipe, to limit air leakage, and the need to make a hopper (110) at the user point a pressure vessel.

Description

MATERIALS HANDLING APPARATUS AND METHOD

This invention relates to materials handling apparatus and method, and in particular to handling apparatus and method for solid, particulate materials able to flow under pneumatic pressure.

It is often convenient to hold particulate feedstock material in one or more centrally located silos, and to supply it as required to a user point by means of a pneumatic conveying system in which the materials are confined and transported within a supply pipe. Usually a positive pressure arrangement is preferred, with an above-atmospheric pressure at the entrance to the supply pipe and atmospheric pressure at the exit; negative pressure arrangements are however also known, with atmospheric pressure at the entrance to the supply pipe and a sub-atmospheric

(vacuum) pressure at the exit. For special applications an inert or other gas can be used instead of air as the transporting medium. Particulate materials can be conveyed in this manner over distances exceeding 1000 metres, or at over 400 tonnes per hour.

Those in the art seek to distinguish between two pneumatic pipe conveying systems for particulate solids, but because they overlap there may be difficulty in correctly categorising a particular system:- (a) the "dilute phase" system using large amounts of air to move relatively small amounts of material at high velocities in suspension, and so often known as the "high velocity" system; and (b) the "dense phase" system using a small amount of air to move a large amount of bulk solid material (for instance in closely-associated slugs) and so often known as the "low speed" system . A dilute phase system is usually operated at a pressure less than 1 bar, with less than 20kg of material for each 1kg of air, to convey material at above 20 metres per second; whereas a dense phase system conventionally utilises a pressure of from 1 to 7 bar, with an air loading ratio in the range 20-150kg of material for each 1kg of air, with a material velocity of from 1 to 1 metres/second.

Although dilute phase pneumatic conveying is widely used, dense phase pneumatic conveying has a number of advantages, particularly the relatively gentle handling of heavy abrasive materials, and of non-abrasive solids that cannot tolerate degradation e.g. fragile crystalline and granular materials; nevertheless some degradation and consequent dust formation must be anticipated, and (as with dilute phase conveying) means must be provided to deal with the dust entrained in the air.

In a conventional pneumatic conveying system, useful for solid particulate materials as varied as sand, coal dust, flour, ground animal feedstuffs, powdered milk or sugar, a charge of the material is despatched at intervals from a transporter vessel to the user point. Usually one supply line will serve a number of user points all requiring the same replenishment feedstock, so the supply pipe is fitted with a number of branch pipes (one to each such user point); the entrance to each branch pipe is controlled by a two-way diverter valve adapted to direct the charge into the respective branch pipe; typically the user point will be a storage hopper from which material is withdrawn to feed a production unit, the storage hopper having a material level or weight measuring device connected to a central control which {a} determines when a charge will be despatched, to avoid replenishment feedstock material being despatched from the transporter when none has been called for, {b} if there are calls from two hoppers, selects the user hopper having priority for replenishment, and {c} effects change-over of the respective diverter valve.

There are disadvantages with the known apparatus and method :- {a} a diverter valve and branch line are needed for each hopper or user point; {b} control means are needed to select the diverter valve having priority for receiving the next charge; {c} all the charge is received by one user point, even if another user point also requires immediate replenishment; (d) the diverter valves operate under arduous conditions and are subject to considerable wear needing regular inspection and maintenance; the failure of a diverter valve may cause supply line blockage; {e} each hopper needs dust control means such as an individual filter housing, accessible for filter replacement, or a dust extraction system wherein the dust is withdrawn to a central disposal unit through conduits accessible for settled-dust removal .

The known systems are therefore often expensive to install and inconvenient to maintain. We seek to provide improved apparatus and method.

We thus provide materials handling apparatus comprising a materials-receiving user point and a supply pipe adapted to convey solid flowable particulate material in pneumatic phase to the user point, characterised by a pressure vessel in the supply pipe adapted to retain material transported in the supply pipe, a suppy pipeline inlet into the pressure vessel, a supply pipeline outlet from the pressure vessel, and further characterised by control means adapted alternately to permit and prevent the discharge of retained material from the pressure vessel to the user point. Preferably the apparatus includes means to effect intermittent transportation of successive charges of the material in pneumatic dense phase, said transportation being timed to occur concurrently with the control means preventing discharge to the user point; the control means can usefully include a valve movable between a fully closed and a fully opened condition, suitably a butterfly valve. Usually the user point will be a storage hopper designed to hold a quantity of feedstock material ready for immediate use by a production unit of a process plant.

In a usual arrangement according to the invention there will be a number of hoppers, one or more for each production line, with a pressure vessel for each respective hopper, the pressure vessels being located at spaced intervals along the supply pipe; during a charge conveying cycle, when a pressure vessel has retained sufficient feedstock material so that the material level therein reaches that of the supply pipeline outlet from that pressure vessel, feedstock material will be pneumatically conveyed down the pipe to the next pressure vessel, and so on. The charge will be (at least) sufficient for all the pressure vessels to be filled (or if they have not been required to discharge to remain filled) to their respective supply pipeline outlet level.

We also propose a materials handling method, particularly for handling flowable solid particulate material, which includes the steps of pneumatically conveying material along a pipe, retaining some of the material in a pressure vessel part-way along the pipe, and subsequently releasing the retained material from the pressure vessel to a user point. Preferably the conveying will be in pneumatic dense phase. The user point will conveniently be a receiving unit such as a storage hopper from which controlled quantities of the material are taken, for instance as feedstock for a production unit such as an oven, or for a production line, but the material may be discharged directly to the production line or unit. Usually a number of pressure vessels, conveniently of standard size, will be positioned in series along the pipe, said pressure vessels being topped up (where necessary) successively by retained material from said conveyed material. The invention will be further described by way of example with reference to the accompanying drawings in which:-

Fig.1 is a schematic view, in section, of a known hopper replenished through a branch pipe from a dense phase pneumatic supply line;

Fig.2 is a schematic plan view of a known multi-hopper system;

Fig.3 is a schematic sectional view of apparatus according to the invention, with two process hoppers shown;

Fig.4 is a schematic plan view of the hoppers of Fig.3;

Figs.5A-C are detailed views of modified apparatus, in successive operating conditions;

Fig.6 is a perspective external view of apparatus as in Fig.5

Fig.7 is of an alternative arrangement to that of Fig.4, in which the pressure vessel is in the form of an inclined reception chute feeding a hopper;

Fig.8 is a schematic sectional view and piping diagram for a process plant with 44 ovens, the ovens being in four groups, the supply pipe being in a closed circuit arrangement returning excess material to the supply silo. The drawings are not to scale.

Hopper 10a (Fig. 1) is depicted as receiving a charge of solid, particulate, flowable, feedstock material (shown hatched) from supply pipe 30 (Fig.2) by way of diverter valve 19a (Fig.2) and branch pipe 12a. Branch pipe 12a is connected to hopper headpiece 14 which includes angled plate 16 directing the conveyed material into the hopper.

Material can be withdrawn from the hopper when valve 26 is opened by valve actuator 28, to supply material to a production unit (not shown). The probe 1 is positioned so that when it is uncovered following such withdrawal of material, and signals to the central control 8 that replenishment feedstock is required, sufficient headspace remains in hopper 10a for one complete charge to be accepted. If following receipt of that charge the probe 18 is still uncovered, the diverter valve 19a remains open to branch pipe 12a, and the next charge is also sent into hopper 10a; but if the probe is covered, the diverter valve 19a is closed before the next charge is despatched; thus said next charge will be sent into another hopper e.g. hopper 10b by way of now-opened diverter valve 19b, since this hopper is assumed to have called for replenishment material. Control 8 can select the priority hopper if two or more hoppers are signalling a need for replenishment material.

During topping-up of hopper 10a, air is forced out from above the material and into filter housing 20, where it passes through filters 22 and out through exit 24 to atmosphere.

Figs. /4 are of a modified arrangement according to the invention. By way of example of user points, two storage hoppers 11 a,11 Ob are shown , each of which in accordance with the process requirement can hold several minutes or several hours supply of feedstock, which can be removed as required to feed a unit (not shown) of a production line. Mounted above each hopper is a respective pressure vessel 32a,32b, each of which has a supply pipeline inlet 34 and a supply pipeline outlet 36. In this embodiment the pressure vessels are formed integral with supply pipe 30, but in an alternative embodiment (Fig.5/6) the supply pipe 30 includes separate pipe lengths each sealingly connected to a supply pipeline inlet and/or outlet. Each pressure vessel is closed by a respective cap 38, which carries abutment member 40, in this embodiment in the form of a rod, but in an alternative embodiment shaped as a plate; abutment member 40 acts to break up the dense phase material to ensure it will drop under gravity (as shown into pressure vessel 32b since headroom is available) and that it does not simply bridge the gap between inlet 34 and outlet 36 of a pressure vessel as a self-supporting compacted slug of material, without dropping; in an alternative embodiment, the inlet 34 and outlet 36 are not in alignment, and in a further embodiment member 40 is omitted.

During this cycle, pressure vessel 32a has already been filled to the level of supply pipeline outlet 36, and so feedstock material has been caused by the applied pneumatic pressure to flow over the material retained in pressure vessel 32a and towards downstream pressure vessel 32b, which is shown being filled; when pressure vessel 32b has been filled, the sequence is repeated, until all the pressure vessels are filled and the surplus material discharges from the downstream (exit) end of supply pipe 30.

The sequence is further illustrated in Figs.5A-C. In this embodiment, and as also seen in Fig. , the supply pipeline inlet 34 and outlet 36 are respectively sealingly connected to pipe lengths 30a,30b by annular clamps 31. Hopper 110a has substantially the same volume as pressure vessel 1.32a, to which it is clamped by bolts 33, which simultaneously retain valve housing 125. Valve housing 125 includes valve 126 and valve actuator 128; valve 126 is energised by air pressure supplied by a separate pneumatic line (not shown), but in a suitable environment an electrically operated valve can be used, "ressure vessel 132a is fitted with shelf 35 to form an air space which can be vented through conduit 37.

As seen in Fig.5A, hopper 11 a is empty, having for instance recently been installed or replaced. Valve 126 is in the closed position so that feedstock cannot pass into hopper 110a, but material in dense phase is flowing along supply line 30 and has already filled pressure vessel 132a; the feedstock charge for this cycle will be sufficient for all the pressure vessels to be filled e.g. vessels 132a to 132z (not shown) if there are 26 vessels along supply line 30.

A positive pneumatic system is assumed i.e. displacement of the materials charge by a pressure differential, in this embodiment of 7psi above atmospheric, praovided at the supply pipe entrance. Following despatch of a charge the supply pipe 30 is blown clear (Fig 5 ), and the pipe entrance pressure is reduced to atmospheric. In an alternative (full-line) arrangement as also discussed below, rather than the pipe 30 being blown clear following delivery of the charge, the material is allowed to come to rest in supply pipe 30 (and material flow is re-started for the next charge cycle with the assistance of supplementary air injectors 46). In a typical negative pneumatic system, supply pipe 30 entrance will be at atmospheric pressure during the charge cycle and the exit will be subject to a vacuum of 5psi below atmospheric.

Valve 126 is now opened (Fig.5B) as is the corresponding valve in the other pressure vessel/hopper units, to permit material to discharge from the pressure vessel into the hopper. As shown, one charge from the pressure vessel 132a is sufficient to fill hopper 110a to the design level, but in an embodiment with a relatively large hopper several such charges may initially be required; once the production line is running however, the charge frequency is selected so that the hopper does not again become emptied (upon outflow of material from the hopper to a production line between charges) i.e. so that the new or replacement (empty) condition of hopper 110a seen in Fig.5A cannot re-occur. It will also be understood that if a pressure vessel contains more material than is required by its associated hopper (low take-off for the production line), the excess remains in the pressure vessel, requiring less top-up material from supply pipe 30 during the next cycle; the valve actuator 1 8 can close valve 126 even if it has to move against such excess material.

Material flow in pipe 30 is stopped whilst valves 126 are open, by reducing the differential pneumatic pressure between spaced sections of supply pipe 30; although for clarity pipe lengths 30a,30b are shown emptied or blown clear, we prefer a full line system, so material will be resting in these pipe lengths until pneumatic pressure is again built up to re-start dense phase conveying. The dense phase material can be made to flow through supply pipe 30 by any of the methods known in the art. We prefer that supplementary air under pressure is provided by injectors 46 located at spaced positions along pipe 30, since stationary feedstock material can then more readily be re-started into flow; thus the supply pipe can be substantially filled (full line system), even with an intermittent flow cycle regime.

The air and any entrained dust displaced from hopper 110a flows upwardly into pressure vessel 132a and into pipe 30 i.e. it is not allowed to escape to atmosphere from that user point, so that a filtering arrangement at each user point is not needed.

Following material discharge from pressure vessel 132a, as shown in Fig.5C valve 126 is closed; it will be noted from this figure that the level of material in hopper 110a has dropped, since material is shown being removed from hopper 110a in accordance with the feedstock demand of the production line, in this embodiment in dense phase along tube 200 by pneumatic pressure from airpipe 202. Each hopper will have its own airpipe. Pressure vessel 132a has meanwhile been re-filled ready for the next discharge to hopper 110a.

In the embodiment of Fig. 7, two pressure vessels are shown in the form of inclined chutes 332, oppositely angled to either side of supply pipe 30. Chutes 332 lead into respective hoppers 310a,310b which are in flow communication with screw conveyors 350a, 350b feeding by way of conduits 352a, 352b into a unit 360 of a production line. If the unit 360 is a furnace, then a two system arrangement can be used, with one supply line feeding a respective one of the chutes on each furnace and the other supply line feeding the other of the respective chutes, whereby the supply lines can be to either side of the furnaces rather than above the furnaces.

Such a multi-system arrangement may also be desirable if the run or supply pipe length for a single supply pipe system would include too many bends or diversions and thus necessarily be carrying a large quantity of feedstock ample for many cycles. If the arrangement as described above of a full-line single line system is used, then the larger diameter pipe needed to convey the replenishment material to all the pressure vessels means a greater amount of air to dissipate at the end of each cycle; if an alternative conveying system is used requiring the pipe to be blown clear at the end of each cycle, then a greater amount of material destined to be dumped will be uselessly conveyed each cycle.

In one example, the conveying rate in the supply pipe is 3.0 tonnes per hour, the distance of conveying is 250 metres, the pipe diameter is 7.62cm (3inches), and the material conveyed is aluminium oxide of particle size 0.249mm.

Fig.8 is a schematic view of a process plant or factory with eighty furnaces (not shown) in four groups A,R,C,D each of twenty furnaces. Feedstock material is conveyed in dense phase along supply pipe 30 to each of the eighty pressure vessels 432 by transporters 52a, 52b, 52c, 52d assisted by air injectors 46; in an alternative embodiment with the furnaces designed as in Fig.7 there will be one hundred and sixty pressure vessels.

Each group of furnaces have a side-by-side length of about 100 metres, requiring a supply pipe 30 run of about 130 metres. If all eighty ovens were fed as a single group, a greater tonnage rate would be required in supply pipe 30 to top up all eighty pressure vessels 132, and thus a larger diameter pipe and/or a greater pressure.

Transporter 52a receives feedstock material from transporter feed silo 400 which is itself fed from a main silo (not shown but which may include preliminary mixing, cleaning and drying phases) by way of input 401 ; silo 400 acts both to store make-up material in bulk and to receive material returned from line 30.

Air is supplied under pressure to transporter 52a to cause feedstock material to flow in dense phase to the pressure vessels for the ovens of group A, and thus to transporter feed silo 402 and transporter 52b.

Transporter 52b feeds the pressure vessels of group B, with supply pipe 30 leading to transporter feed silo 404, and thus in due course to transporter 52c and the group C pressure vessels, and transporter feed silo 406, for transporter 52d which despatches material to the group D pressure vessels.

The remaining or excess material in the supply pipe 30 i.e. that not used to fill pressure vessels 432 returns to control hopper 408. In this embodiment, control hopper 408 is in flow communication with silo 400, so that there is a closed (loop) material conveying system. In an alternative embodiment, control hopper 408 can be located within silo 400; whilst in a less preferred embodiment, which may be necessary if the returned material is too dusty or has been heat degraded (as by remaining too long adjacent furnaces 360) the material from control hopper 408 can be dumped.

In an alternative embodiment, transporter feed silos 402,404,406 are also supplied from input 401, so that transporter 52a is not required to despatch sufficient material for all the user points. Thus transporter feed silo 402 will receive the excess material not required by the group A pressure vessels, and will be topped up as necessary from input 401.

It will be understood that at the end of a conveying cycle, the discharge valves 126 are opened, allowing the collected material to flow to the user point (hopper 110); if the user point is full, none of the material will flow out of the pressure vessel 32,132,332,432; if the user point is partially full, some or all of the material can flow out of the pressure vessel 432. When the transporter 52a is ready to convey again, the valves 126 are closed; if a pressure vessel 432 is not empty, it will require less material to fill it, and thus a greater residue will be conveyed by way of the succeeding pressure vessels to the end of the loop i.e. to control hopper 408. Thus each user point takes only the amount of material it requires each cycle.

As a further feature of the invention, the amount of material returned to control hopper 408 is used to control the blow rate i.e. if too little material is returned so that a greater frequency of charge despatch is needed, a faster build up of air pressure is arranged at transporter 52a.

Thus if in one example the system is run to convey six tonnes per hour, but one tonne per hour excess is returned, then the despatch rate can be reduced to the five tonnes per hour rate, but will preferably be reduced to an intermediate value (e.g. five and a half tonnes per hour) to ensure that all the pressure vessels 32 are still filled each cycle. Thus the material in the loop control hopper or reception silo 408 will "hunt" between a lower level and a higher level, conveniently monitored by level probes (not shown). This multi-rate despatching system ensures that the system overall can be arranged to convey sufficient material to meet the demand of the pressure vessels, with but a small surplus or excess, which however is use to control the cycle frequency.

The cycle time of the conveying system should be calculated from the ratio of available pressure vessel volume and maximum transporter feed rate. This cycle time should be adhered to, even though some of the pressure vessels may not be in use, since the remaining vessels must not be allowed to empty. The maximum batch size can be calculated from the cycle frequency, and the maximum usage of material from the pressure vessels. Providing the system is designed to cycle at the designed frequency with the maximum batch size, peak material calls can be met. Filters and/or dust extractors are not necessary whilst the feedstock material is within the supply pipe 30, but only at the silos 400,402,404,406. Volume and/or weight monitoring systems are not required at each user point; the material at each user point finds its own level, even if the receiver vessels e.g. 110a,110b are of different capacities (to serve production units with different take-off rates). Because the pressure vessels provide an intermediate storage facility, user points which become depleted do not have to wait several charge cycles before receiving replenishment material i.e. if that user point is of low priority and/or several user points are calling for material, since each hopper 110 can receive replenishment material after any one charge cycle. Means such as probe 18 are not required at each storage hopper in order to provide a demand signal for replenishment material. A branch pipe for each user point is not required. A diverter valve is not needed at the entrance to each branch pipe or line (nor in the alternative, as is possible for full line systems, is an open/close valve needed at the exit of each branch line). Control circuitry to effect priority operation of a diverter valve (or of the open/close exit valve) is not required. Multiple transporters can easily be used in single pipe or multi-pipe systems; transporters of different capacities and/or transporter feed silos of different size (see silo 406) can readily be introduced without need to re-write the priority replenishment programme. Ready and safe access to (eg above or on top of) each user point to replace filters etc is not needed, so that the location of user points can be less dependent on the design requirements for the replenishment conveying system.

It will be understood that the units 32, 132 etc are subject to the line pressure (or line vacuum for a negative pressure system) during a charge cycle, as is supply pipe 30 of which effectively they are a part, and that they must be constructed to withstand this pressure; they are thus referred to herein as pressure vessels. The hoppers 32,132 or equivalent need not be built to withstand this pneumatic line pressure since they are isolated therefrom during a charge cycle by the respective valves 126, and furthermore, often the supply pipe 30 is blown clear after completion of each charge cycle and the pressure allowed to decay to or towards atmospheric before the valves 126 are opened. In alternative embodiments the control valves can be self-operating, typically being spring biassed towards the open condition, and being closed as by line 30 air pressure, or by the material retained in the pressure vessel when pressurised, or by the pneumatic pressure also supplied to those injectors 46 located along the supply pipe or line 30.

Supply pipe 30 can include vertical or upward runs.

Claims

. Materials handling apparatus comprising a materials-receiving user point (200,360) and a supply pipe (30) adapted to convey solid flowable particulate material in pneumatic phase to the user point characterised by a pressure vessel (32, 432) in the supply pipe adapted to retain material transported in the supply pipe, by a supply pipe inlet (34) into the pressure vessel, by a supply pipe outlet (36) from the pressure vessel, and further characterised by control means (126) adapted alternately to permit and prevent the discharge of retained material from the pressure vessel to the user point.

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2. Materials handling apparatus which includes a transporter (52), a user point (200,360), a supply pipe (30), and means to cause material to be transported in the supply pipe from the transporter towards the user point characterised by first (32a) and second (32b) pressure vessels spaced apart along the supply pipe, the first vessel having an outlet (36), the second vessel having an inlet (34), the outlet of the first vessel being connected to the inlet of the second vessel, each vessel being adapted to retain a proportion of the material transported in the supply pipe, and by control means (126) adapted alternately to permit and prevent the discharge of retained material from a pressure vessel to a user point associated with that pressure vessel, discharge of retained material being prevented whilst material is being transported in the supply pipe.

3. Materials handling apparatus according to claim 1 characterised by means to effect intermittent transportation of successive charges of material in pneumatic dense phase along the materials supply pipe, and further characterised in that the control means at each pressure vessel includes a pneumatic valve (126) operated by a valve actuator (128) energised by air pressure from a pressurised air line, the pneumatic valve being held closed during the intermittent transportation, and further characterised in that the user point includes a hopper from which materials can be continuously withdrawn.

4. Materials handling apparatus according to claim 1 characterise-!-, by releasable means (31 ) to seal the respective inlet and the outlet of each vessel to the supply pipe, and in that each vessel is closed by a cap (38) which carries a materials abutment member (40) disposed between the inlet and outlet of that vessel.

5. Materials handling apparatus according to claim 1 characterised in that each vessel includes a shelf (35) located below the inlet and outlet and extending part-way across the vessel, and by conduit means (37) to vent the space below the shelf.

6. Materials handling apparatus according to claim 1 characterised in that a single user point is supplied from two vessels (332) spaced apart along a common supply pipe (30), the vessels being to either side of but at a height above that of the user point.

7. Materials handling apparatus according to claim 1 which includes a plurality of user points, characterised in that the user points are in groups (A, B, C, D) , each group being fed from a respective transporter (52a, 52b,52c,52d) by way of pressure vessels dedicated to each user point, the transporter having an outlet connected to the inlet of the first vessel, the outlet of the last vessel being connected to a receiver silo, the outlet of each vessel except the last being connected to the inlet of another vessel except the first so as to link the vessels in sequential array, and in that air injectors (46) are connected between an outlet and an inlet.

8. Materials handling apparatus according to claim 7 characterised by monitoring means to record the material received by the receiving silo, by one of weight or volume, and by regulating means to vary the despatch of a charge of material from the transporter along the supply pipe by one of weight and volume in accordance with said monitoring means.

9. Materials handling method, particularly for handling flowable solid particulate material, which includes the step of pneumatically conveying material along a materials supply pipe characterised by retaining some of the material in pressure vessels spaced apart along the materials supply pipe, each pressure vessel having an inlet and an outlet forming part of the materials supply pipe, and subsequently releasing the retained material from the pressure vessel to a user point.

10. Materials handling method according to claim 9 characterised by returning material delivered from the outlet of the last vessel along the materials supply pipe to the inlet of the first vessel along the pipe, for re-transmission through the pipe.