GB2106668A - Method and apparatus for controlling a pneumatic feed system - Google Patents

Method and apparatus for controlling a pneumatic feed system Download PDF

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Publication number
GB2106668A
GB2106668A GB08224234A GB8224234A GB2106668A GB 2106668 A GB2106668 A GB 2106668A GB 08224234 A GB08224234 A GB 08224234A GB 8224234 A GB8224234 A GB 8224234A GB 2106668 A GB2106668 A GB 2106668A
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GB
United Kingdom
Prior art keywords
pressure
value
signal
bulk material
counter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB08224234A
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GB2106668B (en
Inventor
Dieter Heep
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Waeschle Maschinenfabrik GmbH
Original Assignee
Waeschle Maschinenfabrik GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Waeschle Maschinenfabrik GmbH filed Critical Waeschle Maschinenfabrik GmbH
Publication of GB2106668A publication Critical patent/GB2106668A/en
Application granted granted Critical
Publication of GB2106668B publication Critical patent/GB2106668B/en
Expired legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
    • B05B7/14—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas designed for spraying particulate materials
    • B05B7/1404—Arrangements for supplying particulate material
    • B05B7/1413—Apparatus to be carried on or by a person, e.g. by hand; Apparatus comprising a container fixed to the discharge device
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B12/00—Arrangements for controlling delivery; Arrangements for controlling the spray area
    • B05B12/08—Arrangements for controlling delivery; Arrangements for controlling the spray area responsive to condition of liquid or other fluent material to be discharged, of ambient medium or of target ; responsive to condition of spray devices or of supply means, e.g. pipes, pumps or their drive means
    • B05B12/085—Arrangements for controlling delivery; Arrangements for controlling the spray area responsive to condition of liquid or other fluent material to be discharged, of ambient medium or of target ; responsive to condition of spray devices or of supply means, e.g. pipes, pumps or their drive means responsive to flow or pressure of liquid or other fluent material to be discharged
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
    • B05B7/14—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas designed for spraying particulate materials
    • B05B7/1404—Arrangements for supplying particulate material
    • B05B7/144—Arrangements for supplying particulate material the means for supplying particulate material comprising moving mechanical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
    • B65G53/00—Conveying materials in bulk through troughs, pipes or tubes by floating the materials or by flow of gas, liquid or foam
    • B65G53/34—Details
    • B65G53/66—Use of indicator or control devices, e.g. for controlling gas pressure, for controlling proportions of material and gas, for indicating or preventing jamming of material
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23K—FEEDING FUEL TO COMBUSTION APPARATUS
    • F23K3/00—Feeding or distributing of lump or pulverulent fuel to combustion apparatus
    • F23K3/02—Pneumatic feeding arrangements, i.e. by air blast
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D7/00—Control of flow
    • G05D7/06—Control of flow characterised by the use of electric means
    • G05D7/0605—Control of flow characterised by the use of electric means specially adapted for solid materials

Abstract

A method and apparatus for dosing particulate bulk material to a continuous gas stream for feeding through a closed conveyor (3) to a burner (1) is described. The pressure values of the gas stream are measured at at least two spaced sensor points (3a, 3b) along the conveyor. The value (P2) obtained at the sensor (3b) downstream is modified to obtain a corrected value (P2') proportionally to the counter- pressure closest to the burner (1). This corrected value P(2') is then subtracted from the value (P1) obtained at the upstream sensor (3a). The resultant ( DELTA p') is indicative of the actual pressure differential across the sensed sector of the conveyor (3), corrected for spurious false readings. This resultant actual pressure differential is then compared with a predetermined desired pressure differential for the system, which is a relationship of the desired counter-pressure and the desired load. The result ( DELTA p) of the comparison is then employed as the control signal for regulation of the bulk material feed device. <IMAGE>

Description

SPECIFICATION Method and apparatus for controlling a pneumatic feed system The present invention relates to a method of and apparatus for controlling a pneumatic feed system for the delivery of particulate bulk material such as fuel, or other reactants to an oven, burner, reactor or the like.
Briefly, it is known to introduce, by automatic means, particulate bulk material from a silo or the like, into a carrier gas stream for conveyance through a feed line, such as a duct or conduit, to a burner or other type reactor. it is essential to maintain the load (It), that is the ratio of bulk material in the carrier gas constant, per unit time for the proper operation of the burner or reactor. To this end, the regulated dosing of the bulk material into the carrier gas is critical.
It has been determined that the loss of pressure between two points along the conveyor line, given a constant carrier gas through-put and concomitantly a constant velocity, for a known bulk material, is dependent on the load (. For proper dosing of the bulk material i.e. for maintenance of a defined and predetermined through-put of bulk material per unit time, in other words for the maintenance of a constant load (It), the difference between the desired value of the pressure differential and the actual measured value of the pressure differential at each of the two points, can be used as a servo-control value by which the delivering mechanism, such as a bucket-wheel feed sluice can be controlled. By thus developing a servo-control value, a control loop, responsive to the through-put load, can be employed to regulate the bulk material delivery mechanism.
The first of the two factors necessary for the effective functioning of the control loop, namely, the quantity of carrier gas per unit of time, can be assured by feeding the carrier gas from a compressor which is kept at a constant pressure. A Laval jet of conventional and known design can be used to satisfy this requirement since, in the case of Laval jets, the carrier gas current is directly determined by the inlet pressure in front of the jet.
The second essential condition for the effective operation of the control loop depends upon the maintenance of a constant counterpressure at the end of the conveyor feed line.
This condition is generally left to chance since in open systems, the counter-pressure is equal to atmospheric pressure acting on the conveyor line. There are, however, instances in which this is not the case, for example, in the pneumatic transport of coal dust into particular types of ovens or reactors designed for the liquification or gasification of the coal. In these applications, the system is operated, not only at very high counter-pressures but, in general, with varying counter-pressures. It is these instances it is especially essential that the dosing of the bulk material per unit of time be kept at predetermined desired values.
In the known systems this is not easily done, since the varying counter-pressures cause a corresponding variance in density and, thus, in the volume of the carrier gas. If, the gas volume decreases, while the sectional area of the feed line or duct remains the same, then the velocity of the carrier gas current will also decrease. Consequently, if all other conditions remain the same, this leads to a small loss of pressure along the given sectorof4he feed line over which the pressure differential is measured, since the measured pressure differential is a function of the velocity of the gas current. The reduction of the pressure differential, however, will be interpreted by the described servo-control system incorrectly, as a reduction of the load, which, in order to correct, will require the increase in the delivered quantity of bulkmaterial with the result that the desired maintenance of the quantity of bulk material delivered per unit time, will thereby not be obtained.
There is thus a need for a generally improved method of and apparatus for regulating the dosing of particulate bulk material delivered to a continuous gas stream for feeding a user such as a burner.
According to one aspect of the present invention there is provided a method of regulating the dosing- of particulate bulk material delivered to a continuous gas stream for feeding a user such as a burner or the like, including the steps of determining the pressure values of at least two spaced points in the gas stream, modifying at least the measured pressure value at the point downstream of the conveyor to obtain a corrected pressure value proportionally to a counter-pressure closest to the user, subtracting the correcting pressure from the pressure value determined at the point upstream therefrom, comparing the resultant of said substantion with a predetermined desired pressure differential value and employing the resultant of such comparison to regulate the dosing of said bulk material.
According to another aspect of the present invention there is provided apparatus for regulating the operation of delivery means for particulate bulk material to a gaseous stream flowing through a conveyor system from an infeed to a user such as a burner, reactor or the like, including means for providing a signal indicative of a predetermined counterpressure level desired for operation of said system, means for providing a signal indicative of the predetermined value of the desired pressure differential between the infeed and said burner, a pair of pressure sensors spaced along said conveyor, each providing a signal indicative of the pressure of said stream at the respective point of said sensor, means for modifying the signal obtained by the downstream one of said sensors to obtain a corrected signal proportionally to the predetermined counter-pressure, means for subtracting the corrected signal from the signal obtained by the upstream sensor, means for comparing the resultant signal of said subtraction with the predetermined. signal indicative of the desired pressure differential to provide a control signal for control of said particulate material delivery means.
Particulate bulk material is dosed to a continuous gas stream for feeding through a closed conveyor to a burner. The pressure values of the gas stream are measured at at least two spaced points along the conveyor, and the value obtained at a sensor downstream is modified to obtain a corrected value proportionally to the counter-pressure closest to the burner. This corrected value is then subtracted from the value obtained at an upstream sensor. The resultant is indicative therefore of the actual pressure differential across the sensed sector of the conveyor, corrected for spurious false readings. This resultant actual pressure differential is then compared with a predetermined desired pressure differential for the system, which is a relationship of the desired counter.pressure and the desired load. The result of the comparison is then employed as the control signal for regulation of the bulk material feed device.
For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic representation of a conveyor system for feeding particulate material to a burner, employing the method and apparatus of the present invention, and Figure 2 is a graphic representation of the dependency of the pressure differential upon the counter-pressure.
Briefly, as seen in Fig. 1, the present invention provides a method and apparatus for comparing a corrected actual pressure differential Ap' with a predetermined desired pressure differential Ap, for the system. From this correction, a signal n is obtained for controlling the delivery device by which the fuel is supplied.
The corrected actual pressure differential Ap' is obtained by sensing the pressure along the fuel conveyor at two points P1 and P2 and correcting at least one of these readings proportionally to the counter-pressure at the end of the conveyor, which counter-pressure is a function of both the predetermined counter pressure P desired in the system and the predetermined load jz desired for the system to operate optimally.
The predetermined pressure differential Ap is the relationship between the counter-pressure P desired in the form of a curve whose parameter is the load y. Such system of curves is shown in Fig. 2.
With this in mind, the appliction of this method and the apparatus for carrying it out will be apparent from Fig. 1. As seen in Fig.
1, a burner 1 is supplied with a fuel such as coal dust from a storage hopper or silo 2 by way of a pneumatic conveyor 3 such as a duct or conduit. A compressor 4 generates a carrier gas stream within the conveyor 3. By use of a compressor such as a Laval jet, the stream is maintained at a constant velocity and quantity at least at the beginning of the conveyor. The fuel, being particulate material, is preferably fed into the gas stream by means of a mechanical delivery device such as a bucket-wheel sluice 5, operated by a motor 6, so that the amount of fuel introduced depends upon the speed of the motor 6. The motor 6 is preferably a variable speed electrical motor.
Spaced along the conveyor 3 are a pair of gas pressure sensors 3a and 3b, adapted to sense the pressure at each point, and provide an electrical signal indicative thereof. The downstream signal P2 is fed to an electric circuit 7 such as a bridge or whye circuit where it is combined with a signal received from a control source, such as a variable potentiometer 8 which has been present with a value corresponding to the desired counterpressure P at which the burner system is to be optimally operated. The circuit 7 is also supplied with a signal received from a second source, such as a second variable potentiometer 9 which has been present with a value corresponding to the desired load ,u intended for the system. The resultant corrected value P2' is fed to a subtraction circuit 10 to which the signal P1 from the upstream sensor 3a is simultaneously fed. The difference between the values of the signals P1 and P2', that is Ap' which is indicative of the actual difference between the values obtained by the sensors 3a and 3b (the iater being modified to take into account the correction relative to the desired load and counter-pressure values) is fed to a comparator 11 where it is compared with the predetermined or rated value simuitaneously fed to it from a control element 1 2 which provides a signal Ap which is indicative of the desired pressure differential.
As a result of the input to the comparator 11, an output signal n is obtained which is fed to the motor 6, controlling its rpm, causing the motor to run at a slower speed, thereby causing the bucket-wheel sluice 5 to provide more or less fuel per unit time to the gas stream.
The required constancy of the fuel, fed into the burner per unit of time is thus assured, since the stream pressure is measured at both of the spaced points 3a and 3b where, in effect, the pressure P2, which varies in proportion to the counter-pressure prevailing at the burner 1 since it is nearer the end of the conveyor line, is corrected in the electrical circuit 7 to the corrected pressure P2'. This obviates the defects of the prior art wherein the change in load was not taken into account and would, in fact, result in an unwanted correction in the feeding of the fuel.
The correction obtained in the electrical circuit 7 follows the following formula: P21 = P2 . f(It). f(P) in which the circuit 7 received on the one hand the predetermined desired value of the counter-pressure P and on the other hand the predetermined desired value of the load y inputs from the adjustable value sources 8 and 9.
From the pressure values of P1 and P2' a corrected pressure differential Ap' is generated in the subtraction circuit 10 forming an input to the comparator 11 which is the actual value if the differential or fall in pressure in the conveyor 3 is compared with the value of lip fed from the control element 12. The signal Ap is directly indicative of the f(It) value obtained as seen in Fig. 2, since the correction is dependent not only on the counterpressure P but also the load g. The output of the comparator 11 therefore produces a control signal in which provides the advantageous correction of the system and which is used to modify the rpm of the drive motor 6 regulating the speed of the bucket-wheel sluice 5.
The desired process and apparatus can be effected in simplified form when the range of the load y within which the installation is to be operated is maintained at a constant load which is not too large. Then the desired adjustable input source 9 can be eliminated, since the load at any one time will then be indicated solely by the control element creating the pressure differential Ap. Thus for the correction of P2 to P2', in the foregoing equation, the factor f(,u) is regarded as constant.
Furthermore, in the simplest case, especially when the counter-pressure P will vary only within relatively small limits, then the factor f(P) can also be regarded as a constant.
Thus, with both f(ll) and f(P), maintained as constant, then the indicated equation can be simplified to P2'= P2 . k; wherein k, in accordance with the above, is equal to K1(/1) . K2(P).
It is also possible to come to the same result i.e. wherein the constancy of the dosage is independent any variation of the counter-pressure P, by correcting for the pressure differential P1-P2 to Ap or by the direct correction of the comparator output n to n'. In this instance the problem is shifted to a range in which more values (for example; P1) must be considered and, if necessary, also corrected.
It will be observed that the process proposed in accordance with the present invention is based upon the knowledge that the relationship between the counter-pressure and the measured pressure differential along a given section of the conveyor can be represented in the form of a system of curves whose parameter is of the load ,u. Since normally a definite load is prescribed and is to be maintained, that curve which applies to the corresponding load can be selected for the system. Furthermore, it is usually the case that the desired value of counter-pressure against which the material is to be conveyed, is also known. Corresponding to this counterpressure is a point on the selected curve.
Since all the curves have only a relatively small change in increment or differential, the increment of the curve at any predetermined point can be used as a constant factor of proportionality for determining the magnitude of the correction value, from the difference from the desired counter-pressure and the actual counter-pressure value.
In Fig. 2 there is illustrated a dependence of a pressure differential Ap equal to P1-P2 upon the absolute value of the counter-pressure P for the various values of a constant load p. It is evident that for changes of P around a predetermined desired value which are not too great and for the values of y which are also at not great variance from each other, previously indicated simplication of the correction is admissible according to which Ap = P k.

Claims (8)

1. A method of regulating the dosing of particulate bulk material delivered to a continuous gas stream for feeding a user such as a burner or the like, including the steps of determining the pressure values of at least two spaced points in the gas stream, modifying at least the measured pressure value at the point downstream of the conveyor to obtain a corrected pressure value proportionally to a counter-pressure closest to the user, subtracting the corrected pressure from the pressure value determined at the point upstream therefrom, comparing the resultant of said substantion with a predetermined desired pressure differential value and employing the result of such comparison to regulate the dosing of said bulk material.
2. A method according to claim 1, wherein the correction value for the pressure in said stream at the point closest to the end of said stream is equal to the pressure value at that point multiplied by a function of the predetermined counter-pressure and a function of the load ratio of said bulk material in said stream.
3. A method according to claim 1 or claim 2 including the step of feeding the gas stream to said conveyor under constant volume and velocity.
4. A method according to claim 2, including the step of determining the predetermined desired pressure differential value as a function between the counter-pressure and load ratio.
5. A method of regulating the dosing of particulate bulk material substantially as hereinbefore described with reference to the accompanying drawings.
6. Apparatus for regulating the operation of delivery means for particulate bulk material to a gaseous stream flowing through a conveyor system from an infeed to a user such as a burner, reactor or the like, including means for providing a signal indicative of a predetermined counter-pressure level desired for operation of said system, means for providing a signal indicative of the predetermined value of the desired pressure differential between the infeed and said burner, a pair of pressure sensors spaced along said conveyor, each providing a signal indicative of the pressure of said stream at the respective point of said sensor, means for modifying the signal obtained by the downstream one of said sensors to obtain a corrected signal proportionally to the predetermined counter-pressure, means for subtracting the corrected signal from the signal obtained by the upstream sensor, means for comparing the resultant signal of said subtraction with the predetermined signal indicative of the desired pressure differential to provide a control signal for control of said particulate material delivery means.
7. Apparatus according to claim 6, wherein the means for modifying the signal obtained by the downstream one of said sensors include means for rendering said signal proportionally to a predetermined desired ratio of particulate material and gas in said stream.
8. Apparatus for regulating the operation of delivery means for particulate bulk material, substantially as hereinbefore described with reference to the accompanying drawings.
GB08224234A 1981-08-28 1982-08-24 Method and apparatus for controlling a pneumatic feed system Expired GB2106668B (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE3134180A DE3134180C2 (en) 1981-08-28 1981-08-28 Method for dosing pneumatically transported bulk material

Publications (2)

Publication Number Publication Date
GB2106668A true GB2106668A (en) 1983-04-13
GB2106668B GB2106668B (en) 1985-04-03

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GB08224234A Expired GB2106668B (en) 1981-08-28 1982-08-24 Method and apparatus for controlling a pneumatic feed system

Country Status (8)

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JP (1) JPS5875218A (en)
BE (1) BE894223A (en)
DE (1) DE3134180C2 (en)
FR (1) FR2511986A1 (en)
GB (1) GB2106668B (en)
IT (1) IT1152363B (en)
LU (1) LU84353A1 (en)
NL (1) NL8203106A (en)

Cited By (4)

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Publication number Priority date Publication date Assignee Title
US5726880A (en) * 1995-05-05 1998-03-10 Ranco Incorporated Of Delaware Method of and apparatus for controlling a process
US5752788A (en) * 1994-11-30 1998-05-19 Nordson Corporation System and method of pumping a constant volume of powder
FR2818667A1 (en) * 2000-12-22 2002-06-28 Truetzschler & Co DEVICE FOR REGULATING THE QUANTITY OF FIBER FLAKES TO BE BROUGHT TO A BOARD
US7524146B2 (en) 2006-11-30 2009-04-28 William Jeffrey Peet Pneumatic uneven flow factoring for particulate matter distribution system

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JPS59124624A (en) * 1982-12-27 1984-07-18 Kawasaki Steel Corp Method for distribution and transport of pulverized/ granular material
JPS61155124A (en) * 1984-12-28 1986-07-14 Kawasaki Steel Corp Powdery granule quantitative transport controlling method
GB8528508D0 (en) * 1985-11-20 1985-12-24 Macawber Ltd Simon Material conveying apparatus
DE3919744A1 (en) * 1989-06-16 1990-12-20 Rieter Ag Maschf Carrier air control
US5143485A (en) * 1989-06-16 1992-09-01 Maschinenfabrik Rieter Ag Transport air control
DE4325044C2 (en) * 1993-07-26 2002-07-18 Itw Gema Ag Powder conveying device, in particular for coating powder
DE19542787A1 (en) * 1995-11-16 1997-05-22 Wacker Chemie Gmbh Self-regulating fluidised transport system
DE19900655C1 (en) * 1999-01-11 2000-10-12 Kurt Wolf Velco Ges Fuer Foerd Bulk material transport equipment, especially for bulk material injection in metallurgical plants, has a flow and pressure monitoring system for regulating a deposit, blockage and coarse particle flushing gas system

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GB556864A (en) * 1941-04-22 1943-10-26 Bailey Meters Controls Ltd Improvements in or relating to the control of apparatus for supplying pulverised gas-entrained solid material
FR2236758B1 (en) * 1973-07-02 1978-12-29 Pechiney Aluminium
JPS5514409A (en) * 1978-07-14 1980-01-31 Babcock Hitachi Kk Vent air processing system
JPS5653307A (en) * 1979-10-02 1981-05-12 Ube Ind Ltd Combustion method for upright firing furnace and burner to execute the same
LU82036A1 (en) * 1979-12-27 1980-04-23 Wurth Anciens Ets Paul METHOD AND INSTALLATION FOR INJECTING QUANTITIES OF POWDERED MATERIALS BY PNEUMATIC ROUTE INTO A VARIABLE PRESSURE ENCLOSURE AND APPLICATION TO A TANK OVEN

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5752788A (en) * 1994-11-30 1998-05-19 Nordson Corporation System and method of pumping a constant volume of powder
US5726880A (en) * 1995-05-05 1998-03-10 Ranco Incorporated Of Delaware Method of and apparatus for controlling a process
FR2818667A1 (en) * 2000-12-22 2002-06-28 Truetzschler & Co DEVICE FOR REGULATING THE QUANTITY OF FIBER FLAKES TO BE BROUGHT TO A BOARD
US6681450B2 (en) 2000-12-22 2004-01-27 Trutzschler Gmbh & Co. Kg Apparatus for regulating fiber tuft quantities supplied to a carding machine
US7524146B2 (en) 2006-11-30 2009-04-28 William Jeffrey Peet Pneumatic uneven flow factoring for particulate matter distribution system

Also Published As

Publication number Publication date
IT1152363B (en) 1986-12-31
DE3134180C2 (en) 1983-11-24
DE3134180A1 (en) 1983-03-17
IT8222826A0 (en) 1982-08-12
NL8203106A (en) 1983-03-16
GB2106668B (en) 1985-04-03
FR2511986A1 (en) 1983-03-04
LU84353A1 (en) 1983-02-28
JPS5875218A (en) 1983-05-06
BE894223A (en) 1982-12-16

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