EP1383697A1

EP1383697A1 - Material handling apparatus and method

Info

Publication number: EP1383697A1
Application number: EP02718408A
Authority: EP
Inventors: Stephen Hoddle; Peter Ward
Original assignee: RMC UK Ltd
Current assignee: Cemex UK Operations Ltd
Priority date: 2001-05-03
Filing date: 2002-05-03
Publication date: 2004-01-28
Also published as: GB2375104A; GB0110921D0; WO2002090221A1; GB2375104B

Abstract

A transport container (10) defining a storage volume (11) for particulate matter having an outlet, means for pressurising (18) the storage volume (11) and means for aerating (16, 17) the particulate matter therein and a discharge valve (23) for regulating the flow of the aerated particulate matter through the outlet, wherein the container (10) further comprises a sensor (50) for detecting vibrations during discharge of said particulate matter and for thereby producing a signal indicating that the discharge valve (23) should be closed so as to prevent over-pressurisation of a receptacle (40) receiving said particulate matter.

Description

MATERIAL HANDLING APPARATUS AND METHOD

The present invention relates to the handling of particulate matter and, in particular, to apparatus and methods used in the transport of powders such as cement powder and filling of receptacles such as silos .

It is common to store bulk quantities of particulate matter such as cement powder in silos. The cement powder is usually conveyed to the silo in vehicular transport containers, such as tankers. The cement powder is then transferred into the silo by means of pneumatic conveyance, the silo having a filling pipe and on occasion isolation valve; which is connected to the tanker discharge line by a flexible hose .

A problem can occur in the filling of such silos wherein the silo may become over-pressurised with resultant damage to the structure of the silo and/or its associated equipment and the potential for discharge of cement powder to the surrounding environment. Silos are particularly prone to over- pressurisation at the point when the tanker and the discharge line to the silo empties. The resistance to flow of the pressurised air through the discharge line is many times less than the resistance to flow of the cement-air mixture. As a result, a high volume ^Λslug' of air is exhausted very quickly from the tanker into the silo. The sudden influx of a high volume of relatively high pressure air into the silo causes rapid over-pressurisation. Tankers are commonly pressurised to a level of 2 bar (29.4 psi), whilst the integrity rating for internal gas pressure of a silo may be as little as 1 psi. In order to minimise this danger, it is common for silos to be fitted with filters which allow excess air within the silo to pass to atmosphere whilst retaining the cement powder within the confines of the silo. However, it has been found that such filters are prone to becoming clogged by the cement powder resulting in a reduction in their efficiency. Also, the size of the filters which may practically be installed in silos is not large enough to deal with the high volume 'slug' of air which occurs on emptying of the tanker and discharge line. As a result, with conventional filters, it is possible for a silo to become over-pressurised when the filter cannot exhaust the volume of air entering the silo (due either to poor maintenance or inadequate size) in as little as five seconds or less.

Due to the potential for damage caused by over- pressurisation, it is common for silos to be fitted with a pressure relief device which may be in the form of a flap valve located on the roof of the silo which is activated by the pressure of air inside the silo working against either a spring or counter-weight which holds the valve closed during normal operation. However, pressure relief devices are designed to be used only as a matter of last resort since their use allows cement powder to be exhausted to atmosphere along with the excess air within the silo. In some countries, it may now a reportable offence for cement powder to be exhausted into the atmosphere in this way. As such, it is not desirable to use pressure relief devices as a normal, every-day method of preventing over-pressurisation of silos. The current practice for the prevention of silo over-pressurisation is by a combination of the manual observation of the flexible discharge line, the rate of change of falling pressure indicated by the tanker pressure gauge or the change in pitch in the aural sound from the tank and transport pipe. However, these methods are not reliable and require an experienced operator-. According to the present invention there is provided a transport container defining a storage volume for particulate matter having an outlet, means for pressurising the storage volume and means for aerating the particulate matter therein and a discharge valve for regulating the flow of the aerated particulate matter through the outlet, wherein the container further comprises a sensor for detecting vibrations during discharge of said particulate matter and for thereby producing a signal indicating that the discharge valve should be closed so as to prevent over-pressurisation of a receptacle receiving said particulate matter.

According to the present invention there is also provided a method of transferring particulate matter from a storage volume of a transport container into a receptacle comprising the steps of: a) pressurising the storage volume; b) aerating the particulate matter; c) operating a discharge valve to open an outlet of the storage volume such that aerated particulate matter is discharged through the outlet and into a discharge line connected to the outlet via a discharge manifold; d) monitoring vibrations of the transport container using a sensor; and e) providing a control system linked to the acoustic sensor to close or semi-close the discharge valve or provide an alarm on receipt of a signal from the sensor indicative of the storage chamber being empty or near-empty so as to avoid over- pressurisation of the receptacle.

Embodiments of the present invention will now be described, by way of- example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of a transport container according to the present invention and a storage silo; and

Figure 2 is a plot of tanker pressure and acoustic sensor response during a typical silo-filling operation.

The present invention will now be described in detail with reference to a tanker for use with cement powder and the filling of a silo with cement powder. However, the present invention is not so limited but also finds use in the filling of other receptacles with other powders and particulate matter.

Figure 1 shows schematically a transport container according to the present invention in the form of a tanker 10 connected to a receptacle in the form of a silo 40. The silo 40 is of a conventional design having an inlet 42 at or near an upper end and a pressure relief device 41 of the conventional type described above.

The tanker 10 defines an internal storage volume 11 which, in the illustrated embodiment, is divided into front and rear chambers 12, 13 (commonly known as

^Spots') by one or more baffle plates (not shown). The baffle plates extend vertically upwardly from the base of the tanker 10 but do not extend fully to the top of the storage volume 11, such that, fluid communication between the front and rear chambers 12, 13 is possible.

An air compressor 24 is provided, normally but not exclusively on-board the tanker 10, which is connected to an air distribution manifold 22. A pressure release device 25 is provided for safety purposes between the compressor 24 and air distribution manifold 22. A discharge conduit 26 extends along the length of the tanker 10 from the air distribution manifold 22 to a discharge manifold 23, normally located at a rear of the tanker 11. A tanker pressurisation line 18 connects between the air distribution manifold 22 and the storage volume 11 of the tanker 10 to allow for the influx of pressurised air from the air compressor 24 into the tanker 10. In addition, front and rear aeration lines 16, 17 connect between the air distribution manifold 22 and the front and rear chambers 12, 13 of the tanker 10.

Each of the front and rear chambers 12, 13 is provided with an outlet at or near a bottom thereof having a discharge valve 14, 15 for regulating the opening and closing of the outlets. The discharge valves 14, 15 may be butterfly valves, pinch valves or similar.

The discharge valves 14, 15 discharge into the discharge conduit 26.

Front and rear transport lines 19, 20 connect between the air distribution manifold 22 and the discharge conduit 26. Typically, the transport lines 19, 20 have a bore of approximately 50mm. The front transport line 19 connects to the discharge conduit 26 slightly downstream of the discharge valve 14 of the front chamber 12 and the rear transport line 20 connects to the discharge conduit 26 slightly downstream of the discharge valve 15 of the rear chamber 13.

A ring jet line 21 connects directly between the air distribution manifold 22 and discharge manifold 23 to supply additional air into the discharge line so as to create a swirling or otherwise turbulent flow. Alternatively, a nozzle arrangement may be provided to achieve the same purpose.

Each of the front and rear aeration lines 16, 17, discharge conduit 26, front and rear transport lines 19 and 20 and ring jet 21 are provided with control valves 28-33 respectively downstream of the air distribution manifold 22. The inlet 42 of the silo 40 is connected to the discharge manifold 23 of the tanker 10 by means of a discharge line 27. Typically, the discharge line 27 has a bore of approximately 100 mm. The discharge conduit 26 and discharge line 27 are normally the same diameter.

An acoustic sensor 50 is mounted on the discharge manifold 23, discharge conduit 26 or their associated mountings. The acoustic sensor 50 is preferably mounted by means of a releasable fastener such as a bolt. Advantageously, the mounting of the acoustic sensor 50 does not require an invasive attachment. In other words, the bores of discharge conduit 26 and flexible discharge line 27 are not intruded upon by the acoustic sensor 50. The acoustic sensor 50 is preferably responsive to vibrations on a wide frequency band from 100 to 600 khz and not necessarily limited to audible frequencies. Alternatively an accelerometer or other sensor capable of detecting vibration may be used. A control system (not shown) controls operation of the tanker 10. The acoustic sensor 50 is connected to a control unit of the control system. In a first, manual embodiment the tanker 10 is provided with one or more indicator lamps and/or audible alarms linked to the control unit which are triggered when the acoustic sensor 50 detects a frequency representing the discharge conduit 26 and discharge line 27 emptying, which in turn is indicative that the storage chamber is empty or near-empty. By 'indicative' is meant that the signal detected by the sensor at the discharge manifold 23 is representative of a condition where the storage chamber is empty or near-empty without the need for a direct measurement of the state of the storage chamber to be taken.

In a second, automatic embodiment the discharge valves 14, 15 are also connected to the control unit to allow for automatic operation of the valves 14, 15 depending on the signals received by the control unit from the acoustic sensor 50. In this case the discharge valves 14, 15 are provided with a powered mechanism for operating the valves, such as 5/3 or 3/2 sol/spring spool valves with the spring actuation being such that the air is routed to the discharge valves to close in the normal, de-energised state. Further, the valves 31, 32 of the transport lines 19, 20 may also be linked to, and automatically operated by the control unit.

In use, a tanker 10 which is filled with cement powder is moved into proximity to the silo 40. The flexible discharge line 27 is then connected to the discharge manifold 23 of the tanker 10. The compressor 24 is then started to provide a supply of pressurised air. The flexible discharge line 27 from the tanker 10 to the silo 40 is then checked for any blockages by blowing air from the compressor 24 through the air distribution manifold 22. The operator listens to the sound produced and checks that the pressure gauge on the air distribution. anifold 23 reads low. The valves 28, 29 of the aeration lines 16, 17 are opened to inject pressurised air into the front and rear chambers 12, 13 so as to aerate the cement powder. At the same time, the valve of the tanker pressurisation line 18 is opened to allow a small amount of 'top compressed air' to enter the storage volume 11 from the air distribution manifold 22 to clean the primary venting filter sock located inside the storage volume 11. The pressurised air pressurises the storage volume 11 to level of up to approximately 2 bar.

Normally, the front and rear chambers 12, 13 are discharged sequentially. For example, the rear chamber 11 may be discharged first. In this case, the discharge valve 15 of the rear chamber 13 is opened and cement powder is discharged through the outlet into the discharge conduit 26 where it is then conveyed pneumatically by the air flow within the discharge conduit 26 towards the discharge manifold 23. In addition, compressed air from the rear transport line 20 entering the discharge conduit 26 just downstream of the outlet valve 15 aids the conveyance of cement powder towards the discharge manifold 23. The cement powder travels in a "semi- dense" phase (plugs of cement interspersed with air) . The cement when discharged from the discharge manifold 23 passes along the discharge line 27 into the silo 40. Discharge of the cement-air mixture causes the discharge manifold 23 to vibrate. These vibrations are detected by the acoustic sensor 50 and electrical signals indicating the frequency of vibration are sent to the control unit.

Figure 2 shows a typically trace of the frequencies F detected by the acoustic sensor 50 during a silo-filling operation along with the discharge pressure P of the tanker 10. (In Figure 2 the time direction is right-to-left as shown by arrow T, i.e. the beginning of the trace is on the right of the figure and the end of the trace is on the left of the figure) . The frequency detected by the acoustic sensor 50 during the majority of the filling operation is relatively constant (section F_κ) with only minor deviations. The same is true of the tanker pressure (section P_κ) . Discharge of the cement powder from the rear chamber 13 continues until the chamber is nearly empty. At this point, the frequency of the vibrations detected by the acoustic sensor 50 at the discharge manifold 23 begins to change. As the discharge conduit 26 and flexible discharge line 27 empty (shown by arrow E) , the frequency of the vibrations rise sharply (section D) .

The signals from the acoustic sensor 50 passes to the control unit of the control system reflect the frequency increase. The control unit is programmed with a threshold frequency which is set sufficiently high so as to account for the normal degree of frequency variation in section F_κ, the 'noise' of the signal, and thereby avoid unnecessary tripping of the control system.

In the manual embodiment, as the frequency signal from the acoustic sensor 50 crosses the threshold figure the control unit responds by sending a signal to activate the indicator lamps and/or audible alarms. An operator then responds by manually closing valve 15 of the rear chamber 13 to stop discharge of pressurised air from within the storage chamber 11 through the discharge valve 15 into the discharge conduit 26.

In the automatic embodiment, as the frequency signal from the acoustic sensor 50 crosses the threshold figure the control unit responds by sending a signal to the mechanism of the valve 15 of the rear chamber 13 to close the valve 15 automatically to stop discharge of pressurised air from within the storage chamber 11 through the discharge valve 15 into the discharge conduit 26. Optionally, the control unit may also send signals to the valves of the transport lines 19, 20 to close these valves either instantaneously or after a discrete time interval to allow the air flow through the transport lines 19, 20 to blow through any cement powder remaining in the discharge line 27. The automated embodiment may also include audible and/or visible alarms for operator information.

The discharge process is then repeated for the front chamber 12. Optionally, the rear chamber 13 may be discharged for a second time following discharge from the front chamber 12 to discharge any cement powder which may have passed over the baffle plates within the storage volume 11 from the front chamber 12 to the rear chamber 13 during discharge of powder from the front chamber 12. Optionally, the discharge valves 14, 15 may be designed to be moveable to a semi-closed position as well as a fully closed position. In the semi-closed position the flow of pressurised air though the valve is low enough not to risk over-pressurising the silo 40 but high enough to allow for blow-through of the discharge line 27 to remove the last traces of cement powder.

The invention is also equally applicable to tankers having three or more chambers or ^Λpots' . It has been found that the speed of response of the acoustic sensor 50 is virtually instantaneous with the discharge conduit 26 and flexible discharge line 27 emptying. The acoustic sensor 50 and the control system is able to prevent any significant volume of pressurised air being discharged to the silo 40 after emptying of the discharge conduit 26 and flexible discharge line 27. In tests, for at least one type of silo, the system has been able to reduce the maximum over-pressurisation experienced by the silo 40 to under 0.4 psi or less and close the relevant discharge valve 14, 15 in less than one second following emptying of the discharge line 27.

The acoustic sensor 50 may also be used to detect blockages in the discharge line 27. A blockage will cause a drop in the detected frequency. The control system may be programmed with a second threshold valve representing a blockage. In the same way as described above, the crossing of this threshold would result in operation of the alarm and/or closure of the valves 14, 15.

In a further embodiment of the present invention, the acoustic sensor 50 is replaced by a pressure transmitter, accelerometer or a vibration monitor installed in or on the discharge conduit 26 or discharge line 27 or their associated mountings. The pressure transmitter, accelerometer or vibration monitor measures directly the localised pressure or vibration caused by the movement of the cement-air mixture. It has been found that at or near the point when the discharge conduit 26 and discharge line 27 empties there is a discernable change in the pressure and vibrations experienced in the discharge conduit 26 and discharge line 27. The pressure transmitter, accelerometer or vibration monitor is linked to the control system of the tanker 10. In the same way as described above the signals from the pressure transmitter, accelerometer or vibration monitor may be used to operate an alarm or automatically operate the discharge valves 14, 15.

Claims

Claims :

1. A transport container defining a storage volume for particulate matter having an outlet, means for pressurising the storage volume and means for aerating the particulate matter therein and a discharge valve for regulating the flow of the aerated particulate matter through the outlet, wherein the container further comprises a sensor for detecting vibrations during discharge of said particulate matter and for thereby producing a signal indicating that the discharge valve should be closed so as to prevent over-pressurisation of a receptacle receiving said particulate matter.

2. A transport container as claimed in claim 1 wherein the storage volume is divided into two or more chambers .

3. A transport container as claimed in claim 2 wherein each storage volume chamber is provided with an outlet and discharge valve.

. A transport container as claimed in any preceding claim wherein each outlet is connected to a discharge manifold and the sensor is mounted on the discharge manifold, discharge line or their associated mountings .

5. A transport container as claimed in any preceding claim further comprising a discharge line connected downstream of the discharge manifold to transfer the aerated particulate matter from the discharge manifold to the receptacle.

6. A transport container as claimed in claim 5 wherein the discharge line has a bore of approximately 100 mm.

7. A transport container as claimed in any preceding claim wherein the means for pressurising the storage volume and aerating the particulate matter is an air compressor or other source of compressed air.

8. A transport container as claimed in claim 7 further comprising an air distribution manifold connected upstream to the air compressor and downstream to the storage volume.

9. A transport container as claimed in claim 7 wherein a transport line is connected between the air distribution manifold and each discharge outlet of the storage volume to aid conveyance of the aerated particulate matter towards the discharge manifold.

10. A transport container as claimed in claim 8 wherein each transport line has a bore of approximately 50 mm.

11. A transport container as claimed in ant preceding claim wherein the sensor is an acoustic sensor.

12. A transport container as claimed in any of claims 1 to 10 wherein the sensor is an accelerometer.

13. A transport container as claimed in any preceding claim further comprising a control system operatively connected to the sensor and an alarm system, wherein the alarm system is activated by the control system on receipt of a signal from the sensor indicative that one or more of the chambers of the storage volume is empty or near-empty to thereby indicate that the discharge valve should be closed.

14. A transport container as claimed in claim 13 wherein the alarm is an audible or visual indicator.

15. A transport container as claimed in any of claims 1 to 12 further comprising a control system operatively connected to the sensor and each discharge valve, the control system being programmed to send a signal to automatically close each discharge valve on receipt of a signal from the sensor indicative that the respective chamber of the storage volume is empty or near empty.

16. A transport container as claimed in any preceding claim wherein each discharge valve is further moveable to a semi-closed position in which the flow rate of aerated particulate matter through the outlet is reduced compared to the open valve position.

17. A transport container as claimed in claim 16 further comprising a control system operatively connected to the sensor and each discharge valve, the control system being programmed to send a signal to automatically move the discharge valve to the semi- closed position on receipt of a signal from the sensor indicative that the respective chamber of the storage volume is empty or near empty.

18. A transport container as claimed in any preceding claim wherein each discharge valve is a butterfly valve.

19. A transport container as claimed in any of claims 1 to 15 wherein each discharge valve is a pinch valve.

20. A transport container as claimed in any preceding claim wherein the sensor detects frequencies in the range 100 to 600 kHz-.

21. A transport container as claimed in any preceding claim wherein the sensor is mounted by means of a releasable fastener.

22. A transport container as claimed in any preceding claim wherein the container is a tanker vehicle.

23. A transport container as claimed in any preceding claim wherein the particulate matter is a powder.

24. A transport container as claimed in claim 23 wherein the powder is cement powder.

25. A method of transferring particulate matter from a storage volume of a transport container into a receptacle comprising the steps of: a) pressurising the storage volume; b) aerating the particulate matter; c) operating a discharge valve to open an outlet of the storage volume such that aerated particulate matter is discharged through the outlet and into a discharge line connected to the outlet via a discharge manifold; d) monitoring vibrations of the transport container using a sensor; and e) providing a control system linked to the acoustic sensor to close or semi-close the discharge valve or provide an alarm on receipt of a signal from the sensor indicative of the storage chamber being empty or near-empty so as to avoid over- pressurisation of the receptacle.

26. A method as claimed in claim 25 wherein the sensor monitors the vibration of the discharge manifold.

27. A method as claimed in claim 25 or claim 26 wherein the control system operates an audible or visible alarm on receipt of the signal from the sensor indicative of the storage chamber being empty or near- empty.

28. A method as claimed in any of claims 25 to 27 wherein the control system operates to close or semi- close the discharge valve on receipt of the signal from the sensor indicative of the storage chamber being empty or near-empty.

29. A method as claimed in claim 28 wherein the discharge valve is closed or semi-closed within 2 seconds of detection by the control system of the signal from the sensor indicative of the storage chamber being empty or near-empty.

30. A method as claimed in claim 28 wherein the discharge valve is closed or semi-closed within 1 second of detection by the control system of the signal from the sensor indicative of the storage chamber being empty or near-empty.

31. A method as claimed in any of claims 25 to 30 wherein the storage volume is pressurised to approximately 2 bar.

32. A method as claimed in any of claims 25 to 31 wherein the over-pressurisation of the receptacle is less than 1 psi.

33. A method as claimed in any of claims 25 to 31 wherein over-pressurisation of the receptacle is less than 0.5 psi.

34. A transport container substantially as hereinbefore described with reference to and as shown in the accompanying drawings.