Technical Field

[0001] The present invention relates broadly to a method and a system for predicting fluidisation in a bulk material. The invention also relates broadly to a method and a system for locating stagnant zones in a bulk material.

Background of Invention

[0002] Bulk materials made up of fine particles and with a low moisture content have a tendency to act as a fluid and fluidise when they are aerated. It is understood that air trapped between the particles acts like a lubricant and weakens bonds between the particles. When fluidisation occurs at an outlet of a gravity operated bin and chute system, it can result in uncontrollable flow or flooding. Gates and seals associated with this type of bin and chute systems are designed to stop the flow of bulk solid materials but are ineffective in controlling flooding of a fluidised material. The fluidised material will flow through any gaps until the remainder of the material in the bin and chute system sufficiently deaerates to once again exhibit bulk solid properties. In current systems fluidisation of bulk materials may be detected on occurrence of the bulk material entering a fluidised state. Fluidisation can for example be detected by a change in wall loads of the bin and chute system.

However, this detection of fluidisation after it occurs has limited benefit in reacting prior to flooding of the bulk material.

Summary of Invention

[0003] According to a first aspect of the present invention there is provided a method of predicting fluidisation in a bulk material, said method comprising steps of:

measuring permeability in the bulk material;

detecting one or more trigger events likely to result in fluidisation of the bulk material;

predicting the likelihood of the onset of fluidisation in the bulk material depending on the measured permeability and the detected trigger events. [0004] Preferably the step of detecting one or more trigger events includes one or more of the following:

i) weighing the bulk material in a storage device within which it is contained to detect the mass of the bulk material in the storage device;

ii) sensing strain on a storage device within which the bulk material is

contained to detect bulk material stresses;

iii) sensing the position of a mobile container within which the bulk material is to be discharged to detect a simulation event;

iv) sensing flow of the bulk material from a storage device within which the bulk material is contained to detect a simulation event.

[0005] Preferably the step of predicting the likelihood of the onset of fluidisation involves calculating said likelihood based on a predetermined algorithm. More preferably the algorithm includes at least the measured permeability and the detected trigger events as variable inputs.

[0006] Preferably the method also comprises the step of assessing material properties of the bulk material and including the assessed properties in predicting the likelihood of the onset of fluidisation in the bulk material. More preferably the material properties include particle size and moisture content.

[0007] Preferably the method also comprises the step of adjusting flow of the bulk material depending on the predicted likelihood of the onset of fluidisation. More preferably the flow is adjusted when the predicted likelihood of fluidisation approaches or reaches a threshold probability value. Even more preferably the step of adjusting flow of the bulk material involves at least part closure of a gate or valve discharging the bulk material.

[0008] According to a second aspect of the invention there is provided a system for predicting fluidisation in a bulk material, said system comprising:

measuring means for measuring permeability in the bulk material; detecting means for detecting occurrence of one or more trigger events likely to result in fluidisation of the bulk material; processing means for predicting the likelihood of the onset of fluidisation in the bulk material depending on the measured permeability and the detected trigger events.

[0009] Preferably the detecting means include one or more of the following:

i) Weighing means operatively coupled to a storage device within which the bulk material is contained and arranged to detect its mass;

ii) Strain gauges operatively coupled to a storage device within which the bulk material is contained, the strain gauges configured to detect bulk material stresses within the storage device;

iii) Position sensors operatively coupled to mobile containers into which the bulk material is to be loaded and arranged to detect a simulation event; iv) Flow sensors operatively coupled to a storage device from which the bulk material is discharged and configured to detect a simulation event.

[0010] Preferably the processing means includes a processor configured to calculate the likelihood of the onset of fluidisation. More preferably said likelihood is calculated based on a predetermined algorithm having at least the measured permeability and the detected trigger events as variable inputs. Even more preferably the algorithm also includes material properties of the bulk material including particle size and moisture content.

[0011] According to a third aspect of the invention there is provided a method of locating stagnant regions in a bulk material, said method comprising the steps of:

measuring permeability in the bulk material at a plurality of locations;

identifying stagnant regions in the bulk material depending on the measured permeability wherein the stagnant regions are located at or proximal the plurality of locations having relatively low measured permeability.

[0012] Preferably the step of measuring the permeability involves exposing the bulk material to a pressurised fluid and detecting a time interval for the pressurised fluid to revert to its steady state pressure. More preferably the bulk material is exposed to a compressed gas at a predetermined charge pressure. Even more preferably the measured permeability is derived from and substantially inversely proportional to the time interval. [0013] Preferably the method of locating stagnant regions also comprises the step of selectively positioning flow means at the located stagnant regions for periodic dislodgement of the bulk material at the stagnant regions to promote flow. More preferably the selective placement of flow means involves selectively mounting air cannons and/or vibrators proximal the located stagnant regions

[0014] According to a fourth aspect of the invention there is provided a system for locating stagnant regions in a bulk material, said system comprising:

measuring means for measuring permeability in the bulk material at a plurality of locations;

processing means for identifying stagnant regions in the bulk material depending on the measured permeability wherein the stagnant regions are located at or proximal the plurality of locations having relatively low measured.

[0015] Preferably the measuring means includes a pressurised fluid source holding a pressurised fluid to which the bulk material is exposed. More preferably the measuring means also includes a timer in communication with a pressure sensor operatively coupled to the pressurised fluid source wherein the timer detects a time interval for the pressurised fluid to return to its steady state after its exposure to the bulk material. Even more preferably the measuring means includes a processor in communication with the timer to derive the measured permeability from the time interval to which it is substantially inversely proportional.

[0016] Preferably the simulation event includes collapsing of a rathole in the bulk material.

[0017] Bulk material is to be understood to include relative fine and dry particulate material including fine minerals such as iron ore and coal, and grain.

Brief Description of Drawings

[0018] In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a method and a system for predicting fluidisation in a bulk material will be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 is a graph plotting permeability versus particle size for a bulk material; Figure 2 is a schematic illustration of a system for predicting fluidisation in a bulk material according to another embodiment of the invention;

Figure 3 is graph plotting pressure versus time for bulk materials of different permeability exposed to pressurised fluid according to one implementation of the invention;

Figure 4 is a schematic illustration of various devices for detecting trigger events likely to cause fluidisation according to an embodiment of the invention.

Detailed Description

[0019] The general steps involved in predicting fluidisation in a bulk material in accordance with an embodiment of this invention involve:

1 . measuring permeability in the bulk material;

2. detecting one or more trigger events likely to result in fluidisation of the bulk material; and

3. predicting the likelihood of the onset of fluidisation in the bulk material

depending on the measured permeability and at least one of the detected trigger events.

[0020] It is understood that the permeability of the bulk material as a function of particle size is represented by the graph of figure 1 . It can be seen that "lumps" have a higher settled permeability compared to "fines". The bulk material permeability is a measure of the bulk material density, level of aeration, or porosity, or the interstitial space between particles in the bulk material. Figure 1 shows for the bulk material a particle size or settled permeability below which fluidisation is likely to occur. It is also understood that moisture content of the bulk material will affect its ability to fluidise where higher moisture contents present a lower risk of fluidisation. For these reasons, the preferred method may also involve assessing the material properties, such as particle size and moisture content, to assist in predicting the onset of fluidisation in the bulk material.

[0021] It has been recognised by the inventors that the measured permeability of the bulk material combined with detection of trigger events together provides an indication of the likelihood of the onset of fluidisation in the bulk material. It is to be understood that one or possibly more of these factors alone is not sufficient to accurately predict fluidisation and flooding whereas the selected combination of measured permeability and detection of one or more trigger events is effective in predicting the likelihood of the onset of fluidisation. This can be considered

somewhat analogous to the well-known fire triangle where the combination of fuel, air or oxygen, and heat or ignition result in fire whereas removal of any one of these factors or sides of the triangle will extinguish the fire.

[0022] Figure 2 schematically illustrates one embodiment of a device for measuring permeability in a bulk material. This measuring means is broadly referenced at 10 and is designed to connect to a storage device 12 such as a bulk material bin, silo or chute. The measuring means or device 10 may be located at various locations on the storage device 12. For example, in one implementation the measuring means may be located at two levels in a lower section of the storage device 12 with four measuring devices located at each level for a total of eight devices dedicated to the bulk material storage device 12.

[0023] The measuring means of this embodiment is in the form of an air cannon and includes a relatively small gas storage vessel 14 connected to the bin 12 to provide pressurised fluid or in this case compressed gas via discharge valve 16. The gas vessel 14 is charged with compressed gas from a compressed gas source 18 via charge valve 20. The measuring means also includes a pressure transducer 22 located between the gas vessel 14 and the discharge valve 16.

[0024] The measuring means undergoes the following intermittent cycle from which permeability in the bulk material is derived:

1 . The charge valve 20 is closed and the discharge valve 16 is opened wherein the pressure in the gas vessel 14 is in a steady state, typically at ambient pressure;

2. The discharge valve 16 is closed and the charge valve 20 is opened;

3. Once the pressure transducer 22 achieves a preset charge pressure the

charge valve 20 is closed; 4. The discharge valve 16 is opened and the pressure transducer 22 monitored to determine the time interval for the pressure to return to the steady state;

5. Once the steady state pressure is reached steps 2 to 4 can be repeated at predetermined intervals.

[0025] Figure 3 graphically depicts pressure recorded by the transducer 22 in the course of the preceding cycle used to measure bulk material permeability. The graph illustrates data for materials of different permeability and has been annotated with reference numerals in brackets corresponding to the steps of the preceding pressure cycle. The pressurised air is injected into a mass flow region of the bin 12 at strategically chosen locations.

[0026] It can be seen from the graph of figure 3 that the time interval for the pressure to return to steady state for a high permeability material is less than that for a low permeability material. That is, the injected air dissipates more quickly in the high permeability bulk material. In this example the high permeability material returns to steady state pressure at around 0.5 seconds whereas the low permeability material returns to steady state pressure after around 1 .5 seconds. The permeability of the material is thus inversely proportional to the time interval and can be empirically determined from the time interval.

[0027] In predicting the onset of fluidisation the measured permeability is to be combined with one or more detected trigger events. The trigger events that can for example cause a rapid increase in aeration of the bulk material leading to fluidisation and flooding include:

1 . low material level in a storage device;

2. funnel flow within the storage device;

3. flow rate changes through the storage device.

[0028] Figure 4 schematically illustrates parts of a Train Load Out (TLO) system 30 including various devices for assisting in the detection of the onset of fluidisation.

[0029] In the case of low material levels, bulk material free-falls into the storage device from a feed conveyor and becomes highly aerated. The low level of bulk material in the storage device results in increased aeration due to a longer free-fall. Although the material may deaerate as it sits in the storage device if the level is low and the storage device is simultaneously emptied a relatively short settling time minimises the period for the bulk material to deaerate. In a preferred embodiment of the present invention the system for predicting fluidisation thus includes weighing means operatively coupled to the storage device and arranged to detect the mass and thus the level of bulk material in the storage device. In the TLO system 30 of figure 4 the weighing means includes load cells 32A to 32D mounted to respective of the support legs 34A to 34D of the TLO system 30.

[0030] In the case of funnel flow, a large amount of stagnant material around the sides of a storage device creates a relatively narrow flow channel which reduces the time the material has to deaerate. Additionally, if the stagnant material creates a flow channel in the form of a rathole its collapse can force pressurised air into the material at the bin's outlet further aerating it and promoting fluidisation and flooding. The TLO system 30 of the preferred embodiment may thus provide strain gauges 36A to 36C coupled to the walls 38 of the storage device or chute 40 and designed to detect bulk material stresses on the storage walls 38 indicative of levels of stagnation within the chute 40.

[0031] Flow rate changes where a rapid reduction in flow rate from the storage device causes a rapid deceleration of material which can result in a simulation event such as a rathole collapse. This rapid reduction in flow rate may occur in the transition from a flood to a choke phase. This simulation event will also aerate the material near the bin outlet risking fluidisation of the bulk material. The system of the present invention thus includes detection means for this trigger event in the form of :

1 . Flow sensors such as 42 arranged to detect flow from the storage device; and/or

2. Positions sensors 44A to 44C arranged to communicate with mobile containers into which the bulk material is loaded to detect stages in the flow cycle more susceptible to fluidisation or a simulation event leading to fluidisation and flooding, for example detection of train or wagon speed and/or position. [0032] The onset of fluidisation is predicted in the preferred embodiment based on the measured permeability exceeding a threshold value combined with the existence of one or more of the trigger events. The permeability threshold may be factored upward if more than one of the trigger events is in existence. Alternatively the permeability threshold value may be factored down when two or more triggering events are in existence. The trigger events may also be weighted where trigger events that are more likely to contribute to fluidisation are weighted higher than trigger events less likely to result in fluidisation. The system of the invention may include a processor configured to calculate the onset of fluidisation based on a predetermined algorithm having the measured permeability and the detected trigger events as variable inputs.

[0033] In its preferred form the method and system involve adjustment of flow of the bulk material depending on the predicted likelihood of the onset of fluidisation. The system is likely to include a safety factor to ensure that the flow of bulk material is not unnecessarily disrupted when fluidisation is unlikely to occur. In one embodiment the system may involve at least part closure of a gate or valve discharging the bulk material when the onset of fluidisation is detected.

[0034] In another aspect of the invention the permeability of the bulk material is measured at a plurality of locations. The measured permeability at each of the locations is then used to identify stagnant regions within the bulk material.

[0035] In bulk material storage where funnel flow can occur in a storage bin large zones of material can become stagnant. This stagnation of bulk material can form stable ratholes that will not flow by gravity alone. The live capacity of the bulk material storage bin is thus largely decreased and the stagnant material can degrade over time.

[0036] In a preferred form of this other aspect of the invention flow means is strategically or selectively located in the storage device at regions in the storage device or bin identified as being most susceptible to stagnation. These stagnant zones are identified by measuring permeability of the bulk material at multiple and predetermined locations in the storage device. The measuring means or device of the preceding embodiment may be used in identifying or mapping these stagnant regions having relatively low permeability.

[0037] In a preferred embodiment the flow means provides external forces to the stagnant material to dislodge it and thus promote flow. The flow means may take the form of a vibratory element mounted to a side wall of the storage device proximal the identified stagnant zones, or a pressurised gas device such as an air cannon. In this example the air cannon may locate at or proximal a side wall of the storage device where the permeability measurement identifies a stagnant region or zone.

[0038] It is likely that once the storage device has been zoned for stagnant regions based on permeability measurements at predetermined locations, the various measurement devices can be removed from the storage device. Alternatively the various measurement devices can remain mounted to the storage device for ongoing identification of stagnant regions of bulk material in the storage device.

[0039] Now that a preferred embodiment of the invention has been described it will be apparent to those skilled in the art that the method and system for detection of fluidisation in the bulk material have at least the following advantages:

1 . It is possible to identify fluidisation in advance so that steps can be taken prior to its onset;

2. The system for detecting fluidisation can be retrofitted to existing storage

devices;

3. The system can be integrated with existing control systems to control flow of bulk material to mitigate the risk of fluidisation;

4. The method and system are designed to effectively detect fluidisation with limited risk of contributing to its onset.

[0040] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, the means for measuring permeability need not be limited to the particular arrangement described but may extend to other techniques suitable for measurement of bulk material permeability. For example the permeability may be measured by detecting pressure drop across the material exposed to a set flow of fluid. There may be trigger events other than those specifically described which in combination with measured permeability will effectively predict the onset of fluidisation. The system may also include one or more cameras arranged to detect the trigger events. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.