AU629083B2

AU629083B2 - Apparatus for dense phase conveying of dry solids

Info

Publication number: AU629083B2
Application number: AU68605/91A
Authority: AU
Inventors: Richard James Creswick
Original assignee: COLBY ENGINEERING Pty Ltd
Current assignee: COLBY ENGINEERING PTY Ltd
Priority date: 1990-01-03
Filing date: 1991-01-03
Publication date: 1992-09-24
Anticipated expiration: 2011-01-03
Also published as: AU6860591A

Description

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S F Ref: 117546 aI'lil FORM COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int. Class Application Number: Lodged: PJ8074 3 January 1990 Accepted: Published: Priority: Related Art: Name and Address of Applicant: Colby Engineering Pty. Limited South Creek Road Dee Why New South Wales 2099

AUSTRALIA

Richard James Creswick Actual Inventor: Address for Service: Spruson Ferguson, Patent Attorneys, Level 33 St Martins Tower, 31 Market Street, Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Apparatus for Dense Phase Conveying of Dry Solids The following statement is a full description of this invention, including the best method of performing it known to me/us S019244 03/01/ 9 1 5815/2

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1 2 APPARATUS FOR DENSE PHASE CONVEYING OF DRY SOLIDS Field of the Invention The invention pertains to dry product conveying and more particularly to an apparatus and method for dense phase conveying of fragile powders or granules in a pipe or tube.

Background of the Invention By minimizing the velocity of powdered or granular products being conveyed by a pressure differential, the damage to the product is greatly reduced. The damage to fragile products such as coffee or milk powder in conventional conveying is caused by particle movement and particle contact with the conveying tube or pipe wall.

In the case of milk powder, its ability to readily dissolve is closely related to maintaining the agglomerated structure and not damaging it.

'15 Obiect of the Invention I 4 0> 0'

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0004 t It is an object of the invention to provide an apparatus and method which substantially ameliorate the disadvantages of prior art conveying.

Siimmary of thp Inventinn A positive or negative pressure system causes a product to move in a dense phase along a transport tube or pipe by controlling the product velocity.

In alternate embodiments, the transport system may be used to lift, lower or convey a product within the parameters of that particular "I product's characteristics and physical system layout.

Brief Description of the Drawings Figure 1 is a schematic view of a negative pressure dense phase system.

Figure 2 is a schematic view of a positive pressure dense phase i system.

Figure 3 is a cross-section of a transport tube showing a velocity sensor.

Figure 4 is a plan view of a density sensor used in conjunction with the present invention.

rhk/0310E -3- Best Mode Other Embodiments of the Invention Description of Operation Negative Pressure As shown in Figure 1, product fed into the infeed hopper (1) continues until it reaches a first level probe The powder pump transport controls will then commence operation. First, the vacuum control valve 16 closes, increasing the vacuum at the base of the infeed hopper A few seconds later the powder commences to move through, preferably, 100mm diameter stainless steel lengths of transport tube The product velocity sensor transmits the velocity of the product to a micro-processor and once the product velocity is known it is then possible to control the product flow and pressure in the vacuum at a constant velocity. The velocity sensor may be selected from any number of conventional types such as thermal dispersion types, turbine meters, paddle wheels, strain gauge types, deflection meters or various capacitive method 15 devices. By determining at what velocity product degradation occurs, in a given tube size, the microprocessor can be programmed to regulate the velocity of the dense phase in the transport tube(s) to below that level.

In addition to conventional velocity sensors, a particular and new form has been developed for use in conjunction with the present invention.

As shown in Figure 3 the aforesaid velocity sensor (30) includes a vibration sensing device (31) which would typically be an accelerometer.

The vibration element (32) would normally be a piece of tube mounted at either end between vibration isolation mounts The output of the I sensing device (31) would be directly related to the vibration of the sensing device and as the velocity of the product increased in the tube the output would vary in some ratio. The sensing device detects amplitude and frequency of vibration. By using an interface the output of the velocity sensor can be suitably filtered and amplified to produce an acceptable Input to the printed circuit control board.

If the flow in the system is stopped and then activated again another sensor checks for movement In the system and if no movement is sensed, the multiple injection points will fire sequentially starting from the separator at critical points. The purpose of these inject pulses, which are approximately 0.5 seconds long, are to reduce the static friction and Initiate flow. Once flow has recommenced, the inject points do not operate. In some systems the Inject points may never operate.

rhk/0310E it -4- The product is then drawn into the separator where the air is removed at the top via a stainless steel mesh approximately 200-300 mesh. In a continuous system, a rotary valve (13) would be located at the base of the separator thus providing an airlock to maintain the high vacuum required in the separator while transferring the powder to the ambient pressure external of the separator. In the separator there are two level probes, LP3 (10) and LP4 LP3 (10) is the level probe used to detect if the product level rises above the pre-set limits, indicating more product is coming into the hopper than is leaving it via the rotary valve (13) If this is the case, the transport is discontinued, demand stopped and simultaneously pulses of air or nitrogen are injected (12) at f the base of the separator, assisting the flow of the product out via the rotary valve The second level probe LP4 (11) is used in So,° co-ordination with LP3 (10) to indicate that the product is actually flowing from the separator An alternative to the rotary valve being used in the separator is a butterfly valve (14) which provides a batch method of transport. This has both advantages and disadvantages. The batch method enables far higher vacuums in the separator which can achieve longer and higher lifts. On the other hand, the butterfly valve (14) can only do a batch of product at 6t44a once. Therefore the time lost in the total operating cycle is dependent on o, 0 the time required to empty the hopper before filling it again. It is a relative figure of the time lost in emptying in relation to the total cycle.

ooA micro-processor operates the control valves which maintain the required flow rates and vacuum levels in order to minimize the product velocity for a given flow-rate.

00 90 0 The printed circuit board with its micro-processor require all the related inputs and outputs including four analogue inputs, from the density sensor the product velocity sensor and two vacuum sensors The unit would have an in-built liquid crystal display for operator interface, displaying alarm messages, set-up procedures etc.

The solids/gas stream then enters the cyclone (a secondary filter) and is set into a spinning motion. This motion has the effect of separating the particles outward and downwards through the influence of centrifugal and gravitational forces. As the solid particles migrate rhk/0310E 2 o 00 0 0 0 0 0 0~ 0*0w downwards to be collected at the base of the lower conical section, the cleaned gas flows upward through the top outlet. A 100mm clear plastic tube is located at the base of the cyclone for fine product removal (19).

At either end are two butterfly valves (20) allowing an airlock and a means for the solid, separated particles to escape.

The conveying gas and solid stream remaining, then pass through the polyester fabric filter (21) unit to further clean the air. The Differential Pressure Switch (22) monitors the amount of dust build up.

The cleaning of this fabric is essential due to a pressure drop which rapidly rises as the filtered dust builds up. However, a small amount of build-up actually increases the collecting efficiency as the gas must pass o through the obstacles in its path.

The vacuum pump (22) used to attain the high vacuum is usually a rotary vane type. It is normally in the range of 250 cubic meters per hour up to 500 cubic meters per hour of free air. At the entrance to the vacuum pump there is a disposable paper filter used to remove the super fine particles from the conveying gas.

Where inert gas is used as the conveying medium, the system can be "closed" by providing a feedback tube from the gas discharge vacuum pump to the infeed hopper.

Description of Operation Positive Pressure SNith reference to Figure 2, product is fed into the preload hopper The product flows into the infeed hopper under the batch control of a butterfly valve Upon reaching the Level Probe 1 limit, the butterfly valve closes, stopping feed into the infeed hopper.

The powder pump transport controls then commence operation. A few seconds later the powder commences to move under the influence of free air positive pressure, introduced into the infeed hopper The product velocity sensor as previously described, transmits the velocity of the product to the micro-processor. Once the product velocity is known it is then possible to control the product flow and positive pressure at a constant velocity.

The density sensor as previously described, located in the transport tube, preferably at the base of the infeed hopper basically performs the task of checking that the transport tube (16) is full of 0000, 0 00 0 1 7 -6o o, aoo

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ld( (fll 1 powdered product. A density reading below the pre-set level, indicates that there is excessive air in the transport system, and it will shutdown.

The density problem may be caused by a rathole in the system. The density sensor detects the consistency of material leaving the infeed hopper As shown in Figure 4, a density sensor may include an infra-red transmitter 200 to one side of a transport tube and one or more infrared receivers 201 opposite the transmitter. A signal is derived from the receivers which is proportional to the density of the material passing through the sensor in the tube. If the product being transported has a low flowability and high cohesive forces between the particles, bridging may occur at the outlet of the infeed hopper. Provided there is adequate product the problem is overcome by injecting either a pulse of air or 0 nitrogen by means of the inject solenoid 1 located near the density sensor. If the rathole is detected for more than 2 seconds, the infeed hopper injection point will be operated. This breaks the rathole and maintains the moving product line in the most dense phase to the density sensor. If the fault Is not removed the demand will be lost and an alarm will be activated.

The flow of product will continue until either the demand is stopped or the density sensor indicates the product to air ratio has fallen below pre-set levels. Also the velocity of the product is controlled so that it may not go above a pre-set limit.

If the flow in the system is stopped and then activated again another sensor checks for movement in the system and if no movement is sensed, the multiple injection points (11) will fire sequentially starting from the receiving hopper (12) at critical points. The purpose of these inject pulses, which are approximately 0.5 seconds long, are to reduce the static friction and initiate flow. Once flow has recommenced, the inject points do not operate. In some systems the inject points may never operate.

The product is then deposited into the receiving hopper (12) where the excess air can escape via a stainless steel mesh (14) (approximately 200-300 mesh) to the breather As can be appreciated from the aforesaid description, the velocity controlled dry product transport system is adaptable to a wide variety of conveying applications.

I I rhk/031 OE _1 -LI/II.CI i CI- -7- Accordingly, while the invention has been described with reference to particular arrangements and apparatuses, these should be understood to be examples, and not limitations to the scope or spirit of the invention as set forth in the accompanying claims.

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Claims

1. A transport system for dry powders comprising: an infeed hopper; a separator; a length of transport tube extending from the bottom of the infeed hopper to the separator; a velocity sensor operatively associated with the transport tube for generating a signal proportional to the velocity of a dense phase dry solid in the transport tube; means for generating a pressure differential between the hopper and the separator; and I .means for regulating the pressure differential, in response to a signal from the velocity sensor.

2. The transport system of claim 1, wherein: the means for generating the pressure differential is a vacuum pump; a vacuum supply tube extending from the vacuum pump to the separator.

3. The transport system of either of claims 1 or 2, wherein: one or more gas injectors are disposed in the transport tube for pulsing air or nitrogen into the transport tube.

4. The transport system of any one of claims 1-3, wherein: the hopper is provided with one or more dry powder level sensors; and means are provided for receiving a level signal from each sensor and regulating an influx of dry powder into the hopper in response thereto. The transport system of any one of claims 1-4, wherein: the separator is provided with one or more level sensors; the means for regulating the pressure differential receiving a level signal from each of the separator's level sensors for regulating the pressure differential in response thereto.

6. The transport system of any one of claims 2-5, wherein: a cyclone is interposed, in the vacuum supply tube, between the separator and the vacuum pump, the cyclone adapted to extract fine particles from the vacuum supply tube.

7. The transport system of any one of claims 1-6, wherein: the separator is provided with a rotary valve for extracting dry powder from a lower extremity of the separator. _Ils~--CIIY~ UI*llii- .l*i 4 9

8. The transport system of any one of claims 2-7, wherein: a feedback tube is provided from a gas discharge of the vacuum pump to the infeed hopper.

9. The transport system of any one of claims 1-8, wherein: a density sensor is provided in the transport tube; a gas injector is provided adjacent to the density sensor; and means are provided for activating the gas injector adjacent to the density sensor in response to a density signal generated by the density sensor. t 4) 9 I tr I t ti 19 The the hopper and the the hopper.

11. The one pulsing air or

12. The the transport means for separator system of claim 1, wherein: generating the pressure differential between the is a source of positive pressure which feeds into transport system of claim 9, wherein: or more gas injectors are disposed in the transport tube for nitrogen into the transport tube. transport system of either of claims 10 or 11, wherein: hopper is provided with one or more dry powder level 1 t sensors; and means are provided for receiving a level signal from each sensor and regulating an influx of dry powder into the hopper in response thereto.

13. The transport system of any one of claims 10-12, wherein: the separator is provided with one or more level sensors; the means for regulating the pressure differential receiving a level signal from each of the separator's level sensors for regulating the pressure differential in response thereto.

14. The transport system of any one of claims 10-13, wherein: the separator is provided with a rotary valve for extracting dry powder from a lower extremity of the separator. The transport system of any one of claims 10-14, wherein: a feedback tube is provided from a gas discharge of the separator to the Infeed hopper.

16. The transport system of any one of claims 10-15, wherein: a density sensor is provided In the transport tube; a gas injector is provided adjacent to the density sensor; and means are provided for activating the gas Injector adjacent to the density sensor in response to a density signal generated by the density sensor, rhk/0310E ir---I- I 10

17. The transport system of any one of claims 1-16, wherein: the velocity sensor comprises a section of tube, suspended at each end between adjacent sections of the transport tube by vibration isolation material, and'having affixed to an exterior portion, a vibration sensing device.

18. The transport system of either of claims 9 or 16, wherein: the density sensor comprises a section of tube having on one side an infrared transmitter and disposed on an opposite side, one or more infrared receivers.

19. A negative pressure dense phase dry solids transport system substantially as hereinbefore described with reference to Fig. 1. A method for dense phase conveying comprising the steps of: establishing a safe velocity for a particular dry particulate matter at or below which, negligible damage to that ma<-'r occurs in a given transport tube diameter; establishing a pressure differential between an infeed hopper and a separator which are interconnected by a transport tube of said diameter; removing a stream of dry particulate matter from the infeed 20 hopper in a dense phase; monitoring the actual velocity of the dense phase particulate matter stream in the transport tube; and varying the pressure differential in response to the actual velocity so that the actual velocity does not exceed the safe !elocity.

21. The method of claim 20, further comprising the step of: firing one or more gas injectors located in the transport tube if the actual velocity falls below a pre-set minimum.

22. The method of either of claims 20 or 21 further comprising the steps of: a o0 o o Sa a o 9o a o 0 o ooo a *0 0 0 *0 0 0 0 0 00 o a a 0 0 0 09 0 00 ft 00« a a «a a 0 0 0 0 O 0t a *r a i «4 monitoring the density of the stream of dry particulate matter in the transport tube; determining whether or not a rathole exists In the stream from the monitored density; and firing a gas injector to eradicate the rathole.

23. The method of any of claims 20-22, wherein: establishing the pressure differential is accomplished by drawing a vacuum from the separator through the transport tube to the Infeed hopper. SIBA4..~i k/LMM/310E 4Tr 11

24. The method of any of claims 20-22, wherein: establishing the pressure differential is accomplished by pressurizing the infeed hopper with gas. The method of any of claims 20-24, wherein: the pressure differential is established in an inert gas which serves as a transport medium for the stream of dry particulate matter.

26. The method of claim 25, wherein: the transport medium recirculates and is conserved, the transport medium thus defining a closed loop, by providing a feed back tube which returns to the infeed hopper.

27. A positive pressure dense phase dry solids transport system substantially as hereinbefore described with reference to Fig. 2. DATED this TWENTY THIRD day of JULY 1992 Colby Engineering Pty. Limited Patent Attorneys for the Applicant SSPRUSON FERGUSON t. 4 t 1