AU1973001A - An apparatus and method for pumping powders and other particulate material - Google Patents

Description

1

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name of Applicants: Actual Inventors: Address for Service: QUEENSLAND CEMENT LIMITED 4ACN 000 668 620) "fid BELLS CONCRETE TANKS PTY LTD (ACN 009 558 123) Stephen Donald VICKERS Peter BELLCHAMBERS CULLEN CO., Patent Trade Mark Attorneys, 239 George Street, Brisbane, QId. 4000, Australia.

Invention Title: AN APPARATUS AND METHOD FOR PUMPING POWDERS AND OTHER PARTICULATE MATERIAL Details of Associated Provisional Application: PQ5137 filed on 17 January 2000 The following statement is a full description of this invention, including the best method of performing it known to us: AN APPARATUS AND METHOD FOR PUMPING POWDERS AND OTHER PARTICULATE MATERIAL This invention relates to an apparatus and a method which allows powders such as cement powders (but not limited thereto) and other solid particulate materials to be pumped for instance from a hopper to a storage container or to a use area.

In particular, the invention relates to an apparatus and a method which uses a peristaltic pump together with a fluidiser to achieve the ability to pump dry powders or other solid particulate materials.

Peristaltic pumps move fluids (liquids, suspensions and gases) by the axially progressive radial deformation of an elastic duct or element, of enclosed cross-section, usually in the form of annular tube, having as essential measurements a bore-size and a wall thickness.

Typically, the radial deformation has taken the form of a 15 localised compression of the element, flattening it so that one flattened section of the wall is brought into fluid-tight contact with the radially opposite section of the wall. The compression may be effected by one or more rollers, 0sliding shoes or oscillating fingers, but the operation is identical: the sealed section is progressed a certain distance along the axial dimension, by suitable movement or succession of the operating members.

9 **.This pushes the contents ahead of the compressed section along the element and the restitution of the elastic material behind the .o S.i compression draws in more fluid to be expelled in turn by a succeeding compression.

Peristaltic pumps are fluid-metering devices that are capable of pumping a wide variety of fluids at an accurate rate with good repeatability.

•~o Corrosives, abrasives, aggressive solvents, foodstuffs, and pharmaceuticals can be pumped without risk of contamination or deterioration of either the pump or the fluid being pumped because the only wetted part is the inside surface of the hose.

The prior art includes several multiple channel peristaltic pump designs that have been used in various laboratory and industrial uses.

Another area where peristaltic pumps have been used is in the application of crop protection materials and fertilizers for agriculture. With the increase of precise chemical use in agriculture, there is a need for rugged, dependable devices that are capable of providing accurate, repeatable metering characteristics, such as those generally provided by peristaltic pumps.

However, the prior art has failed to provide satisfactory performance in the aggressive field environments encountered by agricultural users.

Corrosion, degradation, and abrasion of pump components, as a result of contact with environmental contaminants, are problems with known prior art devices. The results of this contamination are reduced hose life, decreased pump accuracy, and premature bearing failure, resulting in a failure of the pump. Another problem in the present art is a lack of repeatability and uniformity between pumping channels. In so-called "cartridge style" pumps, as described in U.S. Patent No. 4,886,431, each 15 hose is occluded independently by using a floating or adjustable occlusion surface. This allows the user to "fine-tune" occlusion on each hose to adjust the flow rate. This is not a desirable characteristic in field situations where a reasonably accurate flow needs to be reproduced after each disassembly without having to recalibrate every pump channel. The second example is in pumps similar to those described in U.S. Patent No. 3,358,609 in which each channel has a separate non-adjustable occlusion surface. When these pumps are stacked together to create a multiple channel pump, it is difficult to achieve uniformity of flow between each channel because of differences in the individual occlusion surfaces.

Stacked or cartridge style multiple channel peristaltic pumps, such as those described above, require each occlusion surface to be disassembled to replace the encased hose. It would be desirable to have a simplified design where a minimal amount of disassembly is required to access and change hoses, and occlusion clearances remain consistent and fixed, thereby preserving accuracy, after each re-assembly. This ease of serviceability is important to aggressive environment users who change hoses on regular service intervals to minimize the possibility of hose failure.

Peristaltic pumps are preferred for certain applications where it is desirable to pump measured amounts of a fluid or to pump a fluid through tubing while avoiding contact between pump components and the fluid being pumped. In a typical peristaltic pump system, a length of tubing is contacted by a series of pressure rollers that rotate in a circular path. The pressure rollers contact and progressively compress a flexible pump tube at spaced intervals against a surface or raceway so as to flatten or locally reduce the cross-sectional area of the fluid passageway in the pump tube. Preferably, the cross-sectional area of the fluid passageway is effectively reduced to zero lo complete occlusion) as each pressure roller moves over the pumping section of the pump tube. As the pressure rollers continue to roll over the pump tube, the successive flattened portions expand or return to the original cross-sectional area due to the resilience of the tube which generates a subatmospheric pressure in the fluid passageway to draw the fluid therein.

The efficiency and many operating characteristics of a peristaltic :000pump depend on the physical and chemical characteristics of the pump tube.

i' The pump tube generally must have a combination of properties including .flexibility, resilience, durability, resistance to creasing, and resistance to adverse chemical or physical effects, since the pump may be used to pump diverse materials including acids, alkali, solvents, toxic and sterile liquids.

Commercially available peristaltic pump tubes are generally uniformly cylindrical, flexible tubes with a uniform wall thickness which provide a fast :recovery rate of the flattened portion to the normal cross-sectional area. Such pump tubes are normally formed from resilient elastomeric materials such as natural rubber, silicone, polychloroprene, and polyvinyl chloride. Such materials, however, have limited resistance to chemical degradation, thereby restricting the use of pumps using such pump tubes to liquids having minimal degradation effects. Fluoroplastic tubing, which has good corrosion resistance, generally has been found to lack resilience and tends to crease in use, thereby limiting the life of such tubing. U.S. Patent No. 3,875,970 (April 8, 1975) attempted to overcome this problem by providing a pump tube having a thin inner tubular portion of a corrosion resistant material (such as polytetrafluoroethylene) and a thicker outer tubular portion of a resilient elastomeric material (such as silicone, polychloroprene, flexible polyvinyl chloride, natural or synthetic rubber). The overall pump tube remained flexible. Although the design of this pump tube reportably extended the life of the tubing, it has not been as successful as desired and its use in commercially available peristaltic pumps appears to be very limited.

In addition, a variety of pump tubes incorporating various geometric configurations, including multiple layered tubes, have been used in peristaltic pumps. U.S. Patent No. 3,105,447 (October 1, 1963) used a double layered pump tube where both the inner and outer tubes consisted of rubber or an elastomer. The pump tube design allowed a lubricant to be pumped through the space formed between the inner and outer tubes. German Patent 3,322,843 Al (published January 3, 1985) also provided a double layered pump tube with a particularly soft and elastic inner layer and an impermeable outer layer. The inner layer could be formed of silicone, natural rubber, soft polyvinyl chloride, polyurethane, or fluoroelastomer; the outer layer could be formed of polyvinyl chloride, polyurethane, fluoroelastomer, and certain polyethylenes. The pump tube was flexible and maintained a circular cross- •section in the uncompressed state. European Patent Publication 0,470,33 Al (published February 12, 1992) provided a flexible pump tube with an elastic S* reinforcing member or members disposed therein to reduce fatigue failure upon repeated compression and recovery of the tubing. U.S. Patent No.

5,067,879 (November 26, 1991) provided a flexible, single- or multi-layered pump tube having two longitudinally extending notches or groves in the outer surface. The groves are designed to improve the flexing characteristics of the tubing during compression and recovery. Although providing useful and significant advances in the art, each of these just described pump tubes has significant limitations for use in peristaltic pumps, especially for peristaltic pumps for corrosive and other difficult to handle liquids.

Conventional peristaltic pumps also have significant problems associated with the pump tube having a tendency to be pulled through the pump body by the forces exerted on the pump tube by the pressure rollers.

The continuous action of the pressure rollers tends to pull the inlet side of the pump tube into and through the pump housing, thereby increasing the risk of breakage or failure of connection to the liquid source. Peristaltic pump manufacturers have attempted to overcome this problem by modifying their pumps or pump tubes to provide clamps or other holding devices to counteract the tendency of the pump tube to be pulled through the pump.

These devices increase the complexity and cost of the pump and/or pump tubes. Moreover, such devices can themselves fail, thereby allowing the pump tube to be pulled through the pump. Such clamps can also abrade or otherwise damage the pump tube, thereby decreasing its lifetime. It would be desirable to provide a pump tube with a significantly decreased tendency to be pulled into and through the pump without the need for clamps or other holding devices.

Prior art peristaltic pumps, both multiple channel and single channel, clamp flexible hosing at the input and output of the pump or pumping channel. As the hose wears or if there are incompatibilities between fluid and hose, the hose can undergo permanent physical expansion. If the hose is not adjusted to remove this expansion, the limited space in the pump housing can cause the hose to bind and pinch, reducing the accuracy of the pump and causing premature hose failure.

00 Another known type of peristaltic pump uses a pump tube comprising an inner tube and an outer tube each of relatively rigid and hard fluoroplastic material, preferably relatively rigid and hard polytetrafluoroethylene (PTFE). The pumping section of the pump tube which contacts the pressure rollers of the peristaltic pump is preformed or shaped into a flattened, oval-like shape which approximately conforms to the pump tube passageway in the peristaltic pump. The pressure rollers contact and compress the flattened side of the pump tube and, thereby, effect the transport or pumping of the fluid. This pump allows, corrosive, hot, and/or high pressure fluids to be readily handled.

Peristaltic pumps are used to pump concrete slurries, for instance for concrete spraying or pumping or concrete or cement slurries.

The pumps work well as the material to be pumped is a wet mixture containing water or suitable liquid.

Peristaltic pumps however are unsatisfactory or unable to properly or efficiently pump particulate solid materials such as powders, granules, sands and the like. The powder is sucked into the inlet of the pump but has a high coefficient of friction and the pump rotor is unable to squeeze the pump tube with the powder in it. In practice, the rotor either locks and with continued use, the pump burns out or is severely damaged. If the pump can be stopped in time, the pump tube needs to be cleaned for further pumping.

Many powders are moisture sensitive and cannot be mixed with water to form a pumpable slurry. For instance, it is not possible to move dry cement powder from one storage area to another storage area using a peristaltic pump, and it is not possible to mix the cement powder with water as this will form a cement slurry which will set. It is uneconomic to attempt to mix cement powders with other types of liquids which do not set the cement powder as the cost of these liquids is prohibitive and there will be large costs and difficulties involved in separation of the liquid from the cement powder.

•There are many other particulate solids which are also unsuitable for 20 admixture with a liquid in order to provide pumpability through a peristaltic ooooo o- pump.

For this reason, and in the cement industry, bulk cement is still moved using conveyors, venturies or rotary valves but none of these are entirely satisfactory because of the rather low throughput, dust problems and maintenance difficulties with the conveying devices.

The present invention is directed to an apparatus and to a method by which particulate solids such as cement powder can be pumped using a peristaltic pump. The invention finds particular use in pumping particulate solids which cannot be mixed with liquids or are otherwise unsuitable for liquid addition.

After much research and experimentation, it has now been found that a peristaltic pump can be made to pump dry powders or other particulate material if the powders are initially injected with a gas stream.

While not wishing to be bound by theory, it appears that the injection of gas into the powders introduces a level of fluid property to the powders which is sufficient to allow the peristaltic pump to pump the dry powders as a fluid.

In one form, the invention comprises a method for conveying particulate solid, the method comprising fluidising the solid using a gas stream passing the fluidised solid into the inlet of a peristaltic pump, and passing the pumped fluidised solid from the pump outlet to a desired location.

In another form, the invention comprises an apparatus for pumping particulate solid, the apparatus having a peristaltic pump which has an inlet and an outlet, and a fluidising means associated with the inlet and which inserts a gas stream into the particulate solid to fluidise the solid prior to the solid passing into the inlet.

The particulate solid which can be pumped can be any type of powder, granular composition, particulate material, ground material and the like which requires pumping to convey it or to otherwise move it from one area to another area. The invention finds particular suitability with pumping of moisture sensitive cement powders but can be used for other types of moisture sensitive powders such as lime, ground carbonates, moisture 20 sensitive hydroxides and the like. It is considered that a person skilled in the •Qe i art would readily establish what type of material would be useful for pumping in this manner. The invention can also be used for pumping granular material or other type of particulate material which is not moisture sensitive but where there is no reason to initially mix the material with water. For instance, the invention could be used to pump dry sands, ground minerals, and organic products such as seeds and the like.

The material which is to be pumped should be robust enough to survive the passage through the pump. It may be so that more fragile materials such as thin hulled seeds may not be particularly suitable for pumping in the method according to the invention, but it is again considered that a person skilled in the art would be able to determine what type of material would be suitable.

The particle size of the material to be pumped as well as the particle shape can vary. It is found that cement powders can be pumped, as can larger particles such as sand, and it is considered that the pump may even be used for larger particles such as aggregates.

Particulate solids which have different particle sizes can also be pumped. While there may be some particle size separation in the pumping and conveying process, it is considered that the apparatus and method according to the invention would still be suitable for pumping solid mixtures of different particles sizes.

The shape of the material to be pumped can also vary and can comprise smooth surfaces, irregular surfaces, round surfaces, oval surfaces and the like.

The peristaltic pump can be of any suitable type and can be of various sizes depending on the volume and size of the material to be pumped. For instance, cement powders can be pumped using a peristaltic 00 pump having a pump tube of approximately 100mm but it should be appreciated that larger and smaller pumps can also be used depending on the circumstances.

The term "peristaltic pump" should be construed broadly and should include at least pumps which consist of a tube which can be selectively deformed by an external rotor or member to convey material along the tube. The tube is usually circular, but may be oval, flattened or other :shapes. The tube is usually curved about the rotor but peristaltic pumps may also include straight tubes which are deformed by a travelling rotor or other 25 member.

loll* The particulate solid is initially at least partially fluidised using a gas stream. The gas stream can be any suitable gas. The choice of gas will depending upon the type of material to be fluidised. For cement, sand and the like, the gas stream can be dry air. For air sensitive solid material, the gas stream may be dry carbon dioxide, dry nitrogen or other suitable gases.

A mixture of gases may be used if desired. The volume of the gas inserted into the particulate solid should be sufficient to at least partially fluidise the solid. The pressure of the gas can also vary to suit. How the gas is injected into the solid can vary. One common way is to use an air slide, but other devices could also be used.

It is preferred that the particulate solid is fluidised at adjacent or close to the inlet of the pump. In this manner, as the particulate solid adopts a fluid or semi-fluid nature, it can be sucked into the pump for pumping. As the pump inlet has a suction force, the particulate solid is preferably fluidised at a position relative to the inlet such that the suction force is sufficient to suck the at least partially fluidised solid into the pump. In practice, the particulate io solid is fluidised by a device either bolted to the inlet of the pump or very close thereto.

The volume of gas injected into the solid should be such to provide the solid with sufficient fluid properties to be pumped while not adding excessive amounts of gas to the particulate solid as this will result in the pump pumping excessive amounts of gas rather than solid. It is considered that a person skilled in the art would be able to vary the gas pressure and volume to suit efficient pumping of a desired particulate solid.

An embodiment of the invention will be described with reference to the following drawings in which Figure 1 shows schematically an apparatus according to an embodiment of the invention.

Figure 2 shows the apparatus in use.

:*..}Referring to the drawings, there is illustrated an apparatus for 0000 pumping particulate solid. The apparatus includes a peristaltic pump which in the embodiment is of the type having a central rotor (not shown) which presses against an internal flexible pump pipe 11. This type of pump is available commercially. Pump 10 has an inlet 12 and an outlet 13 both fitted with typical couplings to allow various devices to be coupled thereto. In the embodiment, the pump pipe is approximately 100mm in diameter and the rotor rotates at approximately 32rpm. This type of pump can pump approximately 50 tonnes p/hour of slurry or liquid material.

Attached to inlet 12 is a fluidising means which in the embodiment is in the form of an air induction box 14. Box 14 has an air inlet which is connected to pressure hose 16 (see Figure 2) and ultimately to a source of compressed air such as a compressor 17. Compressor 17 supplies air at approximately 10KPa as a high volume low pressure source of air. The air passes into box 14 and into a longitudinal tube which has a nylon webbing on the top. Of course, other types of fluidising means could also be used.

Box 14 has an outlet 18 which is coupled to pump inlet 12, and has its own inlet 19 to which a delivery hose 20 can be attached. Hose 20 feeds from a hopper 21 which holds the solid particulate material such as cement powder.

io (Hopper 21 is an embodiment of the invention only and the solid particulate material can be obtained from other sources as well.) In use, pump 10 is started which causes a suction to form at inlet 12. High volume low pressure air is passed through inlet 15 and into box 14 and at the same time the bottom of hopper 21 is opened up. The pump will suck the solid material through hose 20 and into box 14 and over the air tube inside the box. As the solid material passes through box 14, it becomes

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fluidised by the air and adopts an at least partially fluid nature. At this stage, pump 10 can efficiently pump the dry particulate material through the pump and through outlet 13. A conduit 22 can be attached to outlet 13 to allow the solid material to be pumped into a holding tank, silo and the like 23. It is found that pump 10 is able to pump the solid material to a height of 10 to or possibly even more. It is thought that the entrained air passing through the peristaltic pump maintains the solid in a fluidised and therefore flowable state as it passes through conduit 42 thereby allowing it to be pumped along fairly large distances.

It is found that by fluidising or aerating the solid product, solid particulate material such as cement powders and the like can now be pumped in a closed system and without requiring conveyors, venturies and rotary valves. There is very little dust associated with the pumping and therefore large dust collectors are not required. The pump can operate at much lower energy levels than hitherto known conveying systems.

It should be appreciated that various other changes and modifications may be made to the embodiment described without departing from the spirit and scope of the invention.

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Claims (12)

1. A method for conveying particulate solid, the method comprising fluidising the solid using a gas stream, passing the fluidised solid into the inlet of a peristaltic pump, and passing the pumps fluidised solid from the pump outlet to a desired location.

2. The method of claim 1, wherein the solid is in powder form.

3. The method claim 1 or claim 2, wherein the solid is a moisture sensitive powder.

4. The method as claimed in any one of the preceding claims, lo wherein the solid is selected from lime, carbonates, moisture sensitive hydroxide and cement powder. The method as claimed in any one of the preceding claims, wherein the gas stream comprises dry air.

6. The method as claimed in any one of the preceding claims, 15 wherein the gas stream is injected into the solid adjacent the inlet of the 6o@o pump.

7. The method as claimed in any one of the preceding claims, wherein the gas stream is injected into the solid using a air slide.

8. An apparatus for pumping particulate solid, the apparatus 20 comprising a peristaltic pump which has an inlet and an outlet, and a fluidising So..o •means associated with the inlet and which inserts a gas stream into the one particulate solid to fluidise the solid prior to the solid passing into the inlet.

9. The apparatus of claim 8, wherein the gas stream comprises air. oS The apparatus of claim 9, wherein the gas stream is injected 25 using an air slide. 0* OS

11. The apparatus as claimed in any one of claims 8-10, wherein the pump has a pump pipe having a diameter of approximately 100 mm and a rotor which rotates at approximately 32 rpm.

12. The apparatus as claimed in any one of claims 8-11, wherein the gas stream is supplied at approximately 10 KPa has a high-volume low- pressure source of gas.

13. A method substantially as hereinbefore described with reference 14 to the accompanying drawings.

14. An apparatus substantially as hereinbefore described with reference to the accompanying drawings. DATED this 12 h day of February 2001 R4,, QUEENSLAND CEMENT LIMITED SEC (ACNJ 009 658 520) 1 13 BELLS CONCRETE TANKS PTY LTD (ACN 009 558 123) By their Patent Attorneys CULLEN CO. S**