US3678268A - Bulk density gage and bulk density control system - Google Patents

Abstract

The output of a radioactive source is directed through a moving stream of granular material, e.g., coal on a conveyor, and the radiation passing through is sensed by a detector. The detector generates a pulse signal of which the pulse repetition rate varies with the radiation sensed. The pulses generated are counted in a binary counter, and a timer periodically initiates a read-out of and resets the counter to effect successive counting cycles, whereupon the digital count in each cycle is converted to an analog voltage, the magnitude of which is recorded in terms of bulk density of the coal. The recorder controls the addition of water or oil to the coal to, respectively, lower or increase the bulk density of the coal. Controls are included which guard the system from misperforming when a supply of coal has failed, when the depth of coal on the conveyor belt has been lost, and when the coal is so dense that an application of water is required.

Description

United States Patent Reim et al.

3,678,268 July 18, 1972 [54] BULK DENSITY GAGE AND BULK DENSITY CONTROL SYSTEM Republic Steel Corporation, Cleveland,- Ohio Filed: Nov. 5, 1970 Appl. No.: 87,360

Related US. Application Data Continuation of Ser. No. 720,057-, April l0, 1968,

Assignee:

abandoned.

US. Cl. ..250/43.5 D, 250/52, 250/833 D Int. Cl. ..Glt 1/17, GOln 23/14 Field of Search ..250/43.5 D, 43.5 MR, 83.3 D,

References Cited WATER 27 VALVE OIL VALVE DROP SIMULATING COAL DROP IN OVEN RADIATION 01L HAMHEEMILL x! PADDLE SWITCH Primary Examiner-Morton J. Frome Attorney-Robert P. Wright and Joseph W. Malleck [57] ABSTRACT The output of a radioactive source is directed through a mov ing stream of granular material, e.g., coal on a conveyor, and the radiation passing through is sensed by a detector. The detector generates a pulse signal of which the pulse repetition rate varies with the radiation sensed. The pulses generated are counted in a binary counter, and a timer periodically initiates a read-out of and resets the counter to effect successive counting cycles, whereupon the digital count in each cycle is converted to an analog voltage, the magnitude of which is recorded in terms of bulk density of the coal. The recorder controls the addition of water or oil to the coal to, respectively, lower or increase the bulk density of the coal. Controls are included which guard the system from misperforming when a supply of coal has failed, when the depth of coal on the conveyor belt has been lost, and when the coal is so dense that an application of water is required.

Clains, 15 Drawing Figures OIL FLOW TRANSDUC PM. CYCLE 1,575,232 ZM'QVCLE 1510,720

[q tcYcLE |,24e 205 i CONTROL CONSOLE com. DENSITY (PCP) PATENTEU JUL! 8 I972 346782 SHEU 1 [IF 7 1 27 QQ EQ $31-$10 WATER s OIL FLOW TRANSDUC zq q 100a. /17 OL &.

DROP SIMULATING COAL DROP IN OVEN RADlATION on, IL U VALVE SOLENOID (75 GEIGER TUBE COUNTS $215+ CYCLE 75,252 ZMIQVCLE I07 0 2 }|q+k.cvcl.rs 1,246,205 CONTROL CONSOLE BY J5EE? J. POLL/16K P061587 /7. KEMMEM M/G I v. my? K ATTORNEY PATENTED J L 1 8 I912 3,678,268

sum 2 OF 7 QADIATION QOUNTER L \NPUT 1e 34 74 18 COUNTER RESET COUNTER gouMT HOLDOZESET) Q i 50 w w w 1 WWW;

TO OIL CONTROLLER 4 v PEN MOTOR ENABLE V PEN MOTOR CONTROL Ac POWER 45/ SOURCE E PULSE SHAPER 3 TlMER NWT 4 T I M E R 1 2' 4 a e a 64 125 TIMING Locnc UN\T V I 44 PEN MOTOR COUNT ENABLE HOLD 4% COUNTER RESET PATENTED JUL I 81972 ITNFS RADIATI SHEET 3 OF 7 Q CQUNT QYC LES I LAMP DRlVER AMP I UN |T coqnregz cYq. oumee 22 3o N w H 2 El A 32 TI: I2 E!!! in:

D\GITAL TO ANALOG {OUTPUT CONVERTER 26 3@ FROM HAMMERmLL HAMMERMILL PADDLE w SWITCH RELAY (F1636) Q3 FROM COAL LEVEL 60 (WW @L 70 AUXILIARY LOGIC A F CAUBRATION ASS'Y. 7 {2 NORMAL CYCLE I 1 4 a 14 m: 514, NORM L cVcL NORMAL CYCLE Low CYCLE 5\ OUTPUT mpu'r (20) WPOT (IQ) CYCLE LOGIC UNIT YC o% rw A //l e8 AMPLIHER (CYCLE TIMING LOW CYCLE 11. E1 lNTE-GRATOR TO RELAY R we m, 3a)

PATENTED JUH 8 I972 SHEET 7 0F 7 BULK DENSITY GAGE AND BULK DENSITY CONTROL SYSTEM This application is a continuation of Ser. No. 720,057, filed Apr. 10, 1968, and now abandoned.

The system operates so that water and oil addition rates are varied in accordance with bulk density so long as the bulk density is determined to fall within a predetermined range of bulk densities. Oil and water addition is discontinued in the event that the bulk density falls outside the predetermined range. The addition of oil is automatically discontinued in the event that the bulk density is determined to be outside a preestablished normal range. If the bulk density is above the normal range, water is added until either a maximum water rate is achieved or the bulk density enters the normal range. Further, the water addition rate is varied in accordance with the oil rate as longas the bulk density is within the normal range as follows: (a) if the oil rate exceeds an upper limit, the water rate is decreased and (b) if the oil rate is below a lower limit, the water rate is increased.

A plow for holding the radioactive source is employed. The

- plow has a wedge-shaped forward portion and a forwardly extending prow which serve to direct the granular material past and below the plow.

The system employs a drop of the coal beforeit passes the source of radiation so as to simulate the drop of coal in an oven to which the coal is normally supplied, thereby to present coal for bulk density control in a condition the same as that applied to the oven. A paddle-wheel assembly may be employed for this same purpose by striking the material as it is dropped past the paddle-wheel assembly. Alternatively, a sled assembly that tamps the coal may be employed for such simulation.

BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for measuring and controlling the bulk density of granular material. It has particular application to the measurement and control of the bulk density of coal in a coke oven charging system. Bulk density variations in coking coals has been a problem primarily because of variations in the surface moisture of the coal. As surface moisture increases, and the coal is mixed or handled, the bulk density decreases with a corresponding volume increase. As the surface moisture decreases, and the coal is mixed or handled, the bulk density increases with a corresponding volume decrease. It is now generally recognized that one of the most important factors aflecting the uniformity of coke oven operations and the quality and quantity of coke produced is the bulk density of coal that is charged into the coke oven. Changes in the bulk density of the coal away from an optimum density not only cause irregularity in coke oven heating and in oven pressure, which are reflected in impaired quality of the coke; but it also causes variations in the oven output adversely affecting the coke yield.

It is known that the addition of a small amount of oil to the granular coking coal will significantly increase its bulk density and that the addition of water will significantly lower its bulk density. Accordingly, various methods and devices have been used with rather poor success to control the bulk density of the coking coal by adding varying amounts of oil and/or water in order to obtain and maintain the coal within an optimum bulk density range which has been determined as the range which will yield the greatest quantity of high quality coke without danger of damage to the brick work of the coke oven.

Heretofore, there has been no satisfactory way in which the bulk density of coal could be gaged on a continuous basis to provide a criterion for the automatic addition of water and/or oil to adjust and maintain the bulk density of the coal within a predetermined density range.

Initially the measurement and control of bulk density of the coal was by resort to batch sampling and manually controlled water and/or oil additions, according to which samples of coal removed from a moving conveyor belt were subjected to a laboratory volume weight bulk density test at a remote point.

the handling it gets when charged into the oven. A vital part of v the present system is to simulate this condition prior to gaging by allowing coal to fall the correct distance or to simulate such fall.

A continuous weight-type test for bulk density has also been suggested. According to the latter proposal, a continuous sample stream of coal is diverted from a main flow onto a fixed speed conveyor used to deliver a constant volume of coal over a weight belt to produce a weight signal which is converted into a bulk density reading. Signals from this system have been instrumented to record bulk density and to automatically control water and oil additions to produce a desired bulk density. This system has had the disadvantage, as have all the sampling techniques, of the bulk density measurement being made on a comparatively small sample, wherein the sample bulk density has often varied from the bulk density of the coal actually charged into the coke oven. Moreover, this system requires additional chutes, hoppers, bins, belts and conveyors which add to the cost and complexity of the required equipment.

It has been proposed in the past to automatically detect the bulk density of coal by directing radiation to the coal as it passes a detecting station, and utilizing the detected radiation to control the addition of oil and water to vary the bulk density of the coal. Macdonald et al. U.S. Pat. No. 3,148,971 discloses such a system. This patent does not go into the details of the radiation detector nor the control system, but simply indicates that water and oil rates are increased or decreased in accordance with detected changes in bulk density. In a system to be workable, however, it is not sufficient simply to increase or decrease the rates of water and oil addition. It has been found in the present invention that one of the two fluid components should be varied with respect to the other. Generally the rate of oil addition is considered to be the primary control in the present invention, and the water addition rate is varied not only in accordance with bulk density but also in accordance with the rate of oil addition so as to optimize the control of bulk density. Additionally, it has been found in the present invention desirable to employ digital pulse counting techniques in the detection and control of the bulk density of a granular material. Although digital pulse counting techniques have been employed in the past (see, for example, Willett et al. U.S. Pat. No. 3,136,892 directed to the detection of heart rot in power line poles), the present invention utilizes such techniques in bulk density control and in a novel way to ensure control of a process over a predetermined range of counts representing a permissible range of bulk densities over which control is to take place.

It is an object of this invention, therefore, to provide an improved means for accurately, continuously, automatically and economically measuring and maintaining a uniform predetermined bulk density of granular material such as coal charged into a coke oven, which eliminates the above-mentioned disadvantages.

BRIEF DESCRIPTION OF THE INVENTION This invention contemplates a radioactive source for directing radiation through a moving stream of granular material, e.g., coal, and a radiation detector for measuring the amount of radiation passing through the material. In one embodiment, this invention comprises a plow for leveling coal on a belt carrying the coal to a coke oven, a radioactive radiation source for directing radiation through the coal so leveled, detecting means for receiving radiation passing through the coal, means for determining the bulk density of the coal as a function of the detected radiation, means for indicating and recording the bulk density, and means operable with the indicating and recording means for controlling the addition of water and oil to the coal to change the bulk density of the coal to a desired bulk density.

The invention contemplates dropping the coal by a distance substantially the same as the distance it falls in the coke ovens. This is done before the radiation is directed to the coal so that the coal will be in a condition substantially the same as that in the coke ovens. If it is not advantageous to drop the coal by this distance, different arrangements are proposed herein to make the bulk density the same as in the ovens. One is a sled assembly which bears against the coal, and another is a paddle-wheel assembly which strikes the coal as it is made to fall from one point to another.

Further, the addition of oil and water in the present invention, as noted above, is achieved within a range of permissible bulk densities. As the bulk density varies within the range and outside of the range, changes are made in the addition of oil and water. Straightforward control of water and oiling rates in accordance with detected bulk density is employed, as well as special control of water rate in accordance with oiling rate. Further, safety features to discontinue addition of oil and/or water and oil in the event of a loss of coal are also utilized.

The above and further objectives and novel features of the invention will appear more fully in the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals indicate like parts, and

FIG. 1 is a generalized diagrammatic view of principal components of the system intended to illustrate its basic purpose and operation;

FIG. 2 is a diagram showing the disposition of FIGS. 20 and 2b in respect to each other, illustrating in continuity the electronic bulk density gaging system;

FIGS. 2a and 2b, when taken together as shown in FIG. 2, comprise a block diagram of the electronic bulk density gage system;

FIG. 3 is a diagram showing the disposition of FIGS. 3a and 3b showing in continuity the electrical and pneumatic systems controlling the addition of oil and water to a granular material;

FIGS. 3a and 3b when disposed in respect to each other, as shown in FIG. 3, comprise a diagram of the electrical and pneumatic control system regulating the addition of oil and water to a granular material;

FIG. 4 is a timing chart showing the timing functions of a single timing cycle;

FIG. 5 is a curve showing the relationship between Geiger tube counts and coal density per cubic foot;

FIG. 6 is a perspective view of a sled assembly for varying the bulk density of coal to simulate a drop in an oven and a plow for mounting a source of radiation, all in accordance with the invention;

FIG. 6a is a top view of the plow shown in FIG. 6, broken away in part to show some details inside the plow;

FIG. 6b is a sectional view of the plow of FIG. 6a, taken along the section line 6b-6b of FIG. 6a.

FIG. 7 is a sectional view of the apparatus shown in FIG. 6, taken along the section line 77 of FIG. 6;

FIG. 8 is a sectional view of the apparatus of FIG. 7, taken along section line 88 of FIG. 7; and

FIG. 9 is a perspective view of a paddle-wheel assembly in accordance with the invention for varying the bulk density of coal to simulate a drop in an oven.

DETAILED DESCRIPTION A familiarity with the essential features of the invention can be obtained by reference to FIG. 1 in which the invention has been diagrammatically shown as incorporated in a system for handling coal prior to charging the coal into a coke oven battery. The coal is received at the coke battery site as it comes directly from a mine, storage bins, or a stockyard. A mixture of different coals I0 is delivered on a conveyor belt 11 to a conventional hammermill 12 which crushes the coal and reduces it to a relatively uniform particle coal size. Thereafter, in the particular coal handling system shown, a conveyor 13 transports the coal to and drops it onto a conveyor belt 15 which carries it to the coking ovens.

To achieve a desired operation of the coke oven battery, the coal stream 10 must be maintained at a substantially uniform desired bulk density. Usually, the bulk density desired is the maximum bulk density consistent with safe oven pressures and is normally a bulk density above the minimum density that can be achieved by addition of water to the coal used. The coal received at the hammennill l2 varies widely in bulk density and the bulk density is changed at that point to a desired uniform level by the addition to the coal of small amounts of water from a pipe 16 to decrease the bulk density within certain limits, and oil from a pipe 17 to increase the bulk density within certain limits.

To measure and control the bulk density of the coal stream 10, in accordance with one embodiment of this invention, a system is used in which the coal stream 10 is leveled and the stream of coal is reduced to a uniform thickness by a plow 19 as the conveyor 15 carries the coal forward. The bulk density of the leveled coal stream is measured, and means responsive to the measurement of the bulk density causes the selective addition of oil and water to coal to maintain the density of the coal stream 10 within a predetermined bulk density range. To this end, the coal on the belt 15 is leveled by the plow 19 to produce a level, substantially freely piled longitudinally extending coal stream. The leveling step has the result of efficiently keeping the freely piled solid material in the stream sufficiently leveled to make possible the measurement and control of the bulk density of the coal stream by means of a radioactive source and detector. The details of the plow 19 which provide a parting of the coal past the plow and a leveling of the coal without the hanging up" of the coal on the plow and without the plow catching foreign articles such as wire and the like in the coal, will be described later in connection with FIG. 6.

Prior to the leveling of the coal, the coal is dropped from the conveyor 13 onto the conveyor 15. The height of the drop, which is adjustable by adjustment of the height of conveyor 13 over conveyor 15, is made substantially the same as the drop the coal undergoes in the coke oven. Thus the coal is presented to the plow 19 and is conditioned substantially the same as it is in the oven just prior to combustion. This coal handling procedure is important, since it has been found that effective bulk density control is impossible to achieve without conditioning the coal beforehand to simulate its condition in use. Any drops occurring at other transfer points in the conveying system up to the plow 19 have no eflect, since the bulk density of the coal at any given point in the system is dependent only on the height of the last drop which the coal has undergone. Specifically, when coal falls in a drop, the particles separate, thus erasing any previous drop history. Thus successive drops do not produce additive increases in bulk density. The drop provided from the conveyor 13 to the conveyor 15 just prior to plow 19 thus provides a proper conditioning of the coal at the zone in which bulk density is detected. It should be noted at this point, however, that in the event a conveying system cannot be adapted to provide a drop the same as the drop that the coal undergoes in an oven, the drop may be simulated by apparatus to be described later particularly with respect to FIGS. 6 to 9.

Rays from a fixed predetermined substantially constant strength of radiation from a radioactive source 21 are directed through the level coal stream to a detector 23 on the opposite side of the coal stream and at a fixed distance from the radiation source 21. The detector 23 produces a signal proportional to the radiation passing through the coal stream, and the signal is fed to a measuring, recording and controlling means 25. The recorder-controller 25 measures the bulk density of the coal stream on the basis that the signal thereto is proportional to the bulk density of the coal stream; and the recorder-controller responds to the measurement of the bulk density to actuate valves 27 and 29 to add water and/or oil selectively to the coal fed to the hammerrnill 12, so as to control the bulk density of the coal stream to a predetermined substantially constant amount.

Various types of radiation sources may be used in accordance with the invention, including gamma ray emitting radioisotopes such as cesium 137 or radium. For example, the radiation source 21 may comprise a pellet of radium.

The radiation source 21 produces rays of sufficient strength to penetrate the coal stream and the belt 15, so as to produce a signal from the detector 23 proportional to the radiation passing through the coal stream and the belt. A container 31 holds the source 21, and the container is adjustably supported above the coal stream on the conveyor. The rays of energy from the source 21 are made to irradiate a predetermined portion of the stream.

The detector 23 is located on the side of the coal stream 10 opposite the pellet and at a fixed distance from the pellet 21, so as to receive radiation directed through the coal stream 10 and the belt and to produce an electrical signal corresponding in intensity to the radiation reaching the detector 23. To this end, the detector 23 may be a plurality of Geiger Muller tubes, a scintillation counter or similar conventional apparatus.

Gamma radiation from the pellet 21 is attenuated as the radiation passes through the coal in the coal stream and through the belt and this attenuation, or absorption, is a function of the density of the material between the radiation source and the detector. Since a predetermined portion of the stream is irradiated, and since the coal leveling means 19 causes the thickness of this portion of the coal stream to be substantially constant, the absorption of the gamma rays is a function of the bulk density of the coal stream 10. Thus, the detector 23 is exposed to the variable radiation field produced by changes in the bulk density of the coal stream.

The detector 23 generates a pulse signal, the pulse repetition rate of which is representative of the bulk density of the coal within the stream. The pulse signal is acted upon in the control console 25 throughout a plurality of successive counting cycles. In particular, in each counting cycle, a predetermined range of counts is taken as representing a range of bulk densities within which control of the bulk density may be effected. As an example only, this predetermined range of counts may encompass from 1,246,208 to 1,375,232 pulses counted, representing a coal bulk density variation of from 65 to 43 pounds per cubic foot. Within this range of bulk densities a preestablished sub-range of from 43 to 53 pounds per cubic foot, for example, is considered normal." Such a normal" sub-range of bulk densities may be represented by a pulse count in a counting cycle falling between 1,310,720 and 1,375,232. As long as in each counting cycle the number of pulses counted falls within this preestablished sub-range, the oil and water addition rates at the hammermill 12 are varied in accordance with the count. Specifically, if a low count in a cycle is detected, representing a relatively high bulk density close to 53 pounds per cubic foot, for example, the rate of water addition is increased by suitable actuation of the water valve 27, and oil addition is decreased by actuation of valve 29. If a high count in a cycle is detected, on the other hand, representing a relatively low bulk density near 43 pounds per cubic foot, for example, the rate of oil addition is increased by actuation of the oil valve 29 and water addition is decreased.

If the pulse count falls outside of the preestablished subrange of counts, indicating a variation of the bulk density from the normal range, the mode of control is changed. In the example above, the predetermined range of counts was indicated as varying from 1,246,208 to 1,375,232 pulses. This predetermined range thus encompasses the range of normal" densities as well as other, higher bulk densities. For example, the range of bulk densities represented by pulse counts from 1,246,208 to 1,310,720 may represent a coal bulk density variation from 65 to 53 pounds per cubic foot. This is considered a relatively high bulk density, although one which lends itself to control. Accordingly, if the pulse count is within this range, the oil valve 29 is shut off, discontinuing the supply of oil to the coal. Water is increased by suitable control of the water valve 27 until either a maximum rate of water addition is achieved or until, in a subsequent cycle, the bulk density returns to the normal" range.

In the event that the pulse count is outside the predetermined range of counts, e.g., outside the range of pulse counts 1,246,208 to 1,375,232, an abnormal condition is considered to exist and all water and oil additions are discontinued.

A coal level arm 33 is mounted on the rear of the plow 19 and senses the proper level of coal in the stream 10 on the conveyor 15, sending a signal to the control circuits 25 if the proper level is lost. If the proper coal level is lost at the coal level arm, the oil flow to the coal from the pipe 17 is discontinued as by suitable actuation of the oil valve 29. Similarly, a hammerrnill paddle switch 65 positioned just in front of the hammerrnill l0 detects the application of coal to the hammermill. 1f the switch arm drops, indicating a discontinuance of coal supply to the hammermill, a signal is developed which is applied to the control console 25 for control purposes. Additionally, the signal causes the immediate closure of the water solenoid and the oil solenoid 94 to discontinue all application of oil and water to the coal.

From FIG. 1 it will be noted that an oil flow transducer a is positioned in the oil pipe 17 to provide a signal to the control console 25 representative of the flow of oil to the coal for purposes of bulk density regulation. Within the control console this signal is utilized to control the addition of water to the pipe 16. To elaborate, as long as the control console is counting pulses in each cycle indicating a normal bulk density of from 43 to 53 pounds per cubic foot, for example, the system operates to ensure that oil flow is within a desired range. Specifically, if the rate of oil addition to the coal exceeds an upper limit, the water rate is decreased. If the oil rate is below a lower limit, on the other hand, the water rate is increased. In this fashion, the rate of oil addition is taken as a primary control which is to be established within a certain desired range. The rate of water addition is either increased or decreased, as the case may be, when the oil rate is outside the desired range so as to bring the oil rate within the desired range. Otherwise, the water and oil rates are both varied in each counting cycle so that they are increased or decreased depending upon the variation of bulk density within the "normal range of 43 to 53 pounds per cubic foot, for example, as described above.

In this regard, oil has been taken as the primary control, as just noted. However, water could be taken as the primary control just as easily, with oil varied to maintain the rate of water addition within a predetermined desirable range. Oil has been taken as the primary control since coal typically includes quantifies of water and typically is of too low a bulk density, requiring the addition of oil to raise the bulk density into a desired range.

The operation of the entire system may be presented in tabular form, as given below.

TABLE A 1. Radiation pulse count in each counting cycle is within a normal" range (e.g., representing a coal density of 43 to 53 pounds per cubic foot):

a. The rates of water and oil addition are decreased or increased by control of valves 27 and 29 in accordance with bulk density.

b. The water rate is varied in accordance with the oil rate as follows: (i) if the oil rate exceeds an upper limit, the water rate is decreased; (ii) if the oil rate is below a lower limit, the water rate is increased.

II. Radiation pulse count in any counting cycle is outside of a normal" range (e.g., outside of a coal density range of 43 to 53 pounds per cubic foot):

a. Oil flow from pipe 17 is discontinued by control of oil valve 29.

b. If the radiation count is within a range representing a relatively high bulk density of from 53 to 65 pounds per cubic foot, e.g., water is added until (i) a maximum water addition rate is achieved, or (ii) in the next counting cycle the count enters into the normal range.

c. If the radiation count is not within the range of (b) above (e. g., the bulk density is greater than 65 pounds per cubic foot or less than 43 pounds per cubic foot), water flow from the pipe 16 is discontinued by control of water valve Ill. Lack of coal level:

a. At the hammermill as detected by hammermill paddle switch 65, oil and water flows through pipes 17 and 16 are discontinued by control of water and oil solenoids 95 and 94.

b. At the hammermill as detected by hammermill paddle switch 65 and/or at the coal level arm switch 33 adjacent the radiation source, oil flow is discontinued by control of oil valve 29.

FIGS. 2a AND 2b The determination of the radiation passing through the coal in each of the plurality of successive counting cycles will now be explained. The radiation is detected by the detector unit 23 which may consist of a plurality of Geiger Muller tubes connected in parallel, e.g. The tubes produce voltage pulses when they are subjected to a flux of gamma rays. The number of pulses resulting from the gamma ray interactions with the tubes is proportional to the amount of radiation passing through the coal. An increase in coal density results in a decrease in radiation to the detector, and a decrease in coal density results in an increase in radiation affecting the detector.

The pulses from the detector 23 are transmitted to an amplifier 16 (FIG. 2a) where they are shaped and amplified. The input circuit differentiates the pulses to develop pulses of narrow width. Four transistor stages (not shown) are used, e.g., as a voltage amplifier, producing pulses of about 1 microsecond width and 12 v. in amplitude. The last stage of the amplifier supplies the power to drive the pulses over a coaxial cable to a gage radiation counter circuit 18 (FIG. 2a).

The counting of pulses from the Geiger tubes takes place in each of a continuous series of successive counting cycles or periods. Counting is achieved by three series connected counter circuits in FIGS. 20 and 2b, i.e., counter 18 in FIG. 2a and a unit counter 22 and a cycle" counter 30 in FIG. 2b. The counting period typically comprises 64 seconds, although this time period is arbitrary. During this time the pulses are counted, and the total count is representative of the radiation passing through the coal, i.e., the bulk density of the coal. The counting period is chosen sufficiently long so that random variations in the emission of energy from the radiation source 21 are averaged out over the counting period. That is, the effect of random high and low level radiation is effectively cancelled by virtue of the integration or averaging of pulses achieved by counting over the time period.

The counter circuit 18 is composed of a plurality of bi-stable multivibrators 20 labeled in FIG. 2a as stages 1, 2, 4 1024 indicating the number of input pulses to the first stage required to turn on the respective stage. For example, the stage 16 will be triggered on from its off state after 16 pulses have been received. The counter accumulates pulses from the detector 23 for a discrete time period, e.g. 64 seconds.

The output from the last stage of the counter 18 comprises an input to a unit" counter 22 (FIG. 2b) consisting of six bistable multivibrators 24 labeled as stages 1, 2, 4 32 corresponding to the number of pulses from the counter 18 to turn on the respective stage. One unit corresponds, therefore, to 1024 Geiger tube pulses. The inverse output of each multivibrator stage in the unit counter is connected to corresponding inputs of a digital-to-analog converter 26 and also to individual unit lamps 28 on the control console through lamp driver amplifier 72. The digital-to-analog converter 26 is a conventional switch and summing resistor network (not shown). The bulk density determination is obtained from the data in the six stages of the unit counter 22 at the end of the 64 second counting period, in conjunction with the count in a cycle counter 30, to be explained as follows:

The next six multivibrator stages comprise the cycle counter 30 wherein one cycle" represents 64 units, or 64 X l,024= 65,536 Geiger tube pulses. In this regard, a cycle" as representing a particular number of Geiger tube pulses must not be confused with a timing cycle" of 64 seconds. The output of each stage of the cycle counter is connected to individual cycle lamps 32 on the control console (through amplifier 72) and to the circuits of a cycle logic unit 56. The relationship between pulse counts and bulk density for an exemplary installation is as follows:

43 pounds/ft 63 units and 20 cycles 1,024 X 63 1,024

X 64 X 20 1,375,232 Geiger tube counts 53 pounds/ft 0 units and 20 cycles 1,024 X 64 X 20 1,310,720 Geiger tube counts.

The pulse count versus bulk density relationship is shown in FIG. 5 for an exemplary installation.

Each multivibrator stage of the counters has an output indicating an ON condition, e.g., the right side of the multivibrator is conductive, and an OFF or inverse condition, e.g., the left side is conductive. The ON output may be designated by the number of the stage (1, 2, 4 1024, as in the counter 18) and the OFF or inverse output may be designated by the stage number with a line above it (T, 2, 4.... 1024, read as inverse 1, inverse 2, inverse 4 inverse 1024). The multivibrator stages receive inverse reset signals on lines 34 and 50 (FIG. 2a) which, when energized with appropriate signals, reset the multivibrators to their OFF condition.

It has been stated that the digital-to-analog converter 26 (FIG. 2b) is a switching and summing resistor circuit. This circuit is not shown since it is of conventional design. Its inputs are the six inverse outputs of the unit counter 22, and its output is an analog voltage on the line 36. The output voltage on the line 36 is a DC voltage inversely proportional to the unit counter reading, and it constitutes the input of a bulk density recorder 58. By making the analog voltage inversely proportional to the count in the counter, an analog output signal is generated which increases with increasing bulk density. The count in the counter decreases with increasing bulk density since less radiation is detected by the Geiger Muller tubes. The digital-to-analog converter 26 contains six solid state switches (not shown) each switch being connected to a current source (not shown) proportional to its binary count number. For example, the first switch has a 1 MA current source, the second switch has a 2 MA current source, the third switch has a 4 MA current source, the fourth switch has an 8 MA current source, etc. With the appropriate switches closed, as determined by the signals from the units counter, the currents are summed to produce an output on line 36 proportional to the input signal from the counter 22.

A time base is provided by a timer 38 (FIG. 2a) composed of a plurality, e.g. l2, bistable triggers 40. The input to the timer triggers is derived from a pulse shaper 42 (FIG. 2a). The pulse shaper 42 is typically a conventional two-transistor Schmitt trigger (not shown) whose input is a sinusoidal signal, e.g., at line frequency (60 cps). The pulse shaper provides suitably shaped pulses to the timer 38 at a predetermined rate, e.g., 60 pulses per second. The timer 38, composed of 12 bistable multivibrators connected in series, functions as a simple binary counter. In FIG. 2a, the timer stages are labeled 1, 2, 4 2048, designating the number of input pulses required to operate the respective stages. The timer input, as stated, is a continuous pulse train from the pulse shaper 42. One complete timing cycle has a span of 68.27 seconds, the

time required to apply 4096 input pulses to the timer counter stages. Following reception of pulse 4095, all 12 stages of the timer will be switched ON. The next input pulse will switch all stages to their OFF state, thus conditioning the timer to go through another timing cycle.

The output of each timer stage is connected to a timing logic unit 44 consisting of a plurality of AND circuits (not shown) connected in conventional manner to provide output pulses at preselected intervals in the timing cycle. Following reception of 16 input pulses (in 0.27 second), for example, the multivibrator stage 16 is ON and provides an output signal to the timing logic unit 44. After receiving 3344 pulses (55.73 seconds), the 2048, the 1024, the 256 and the 16 multivibrator stages are ON and provide output signals to the timing logic unit 44. In this manner, timing information can be obtained throughout a range of 17 milliseconds (a count of one input pulse) to 68.27 seconds (a count of 4096 pulses).

The timer unit 38 provides a timing schedule by way of its circuitry for four events which take place during one complete timing cycle (see FIG. 4). Timing pulses from the unit 38 constitute the following signals: PEN MOTOR ENABLE on line 46 connected to a pen motor control circuit 48, COUNT HOLD on line 50 connected to the reset inputs of the first four stages of the counter 18, and COUNTER RESET on line 34 connected to the reset inputs of all but the first four triggers comprising the counter 18 and to all of the triggers of the unit counter 22 and the cycle counter 30. The output of the last four multivibrators of the timer 38 is the signal CYCLE TIM- ING which is transmitted on lines 54 as inputs to a cycle logic unit 56 (FIG. 2b). FIG. 4 shows the timing of the various signals generated by timer 38.

The signal COUNT HOLD on line 50 is developed within the timing logic unit typically by diodes (not shown) connected to stages 256, 512, 1024 and 2048 of timer 38. Four diodes (not shown) comprise an AND circuit, the output switching from 6 V. to V. DC, for example, only when 3840 input timer pulses (64 seconds) have been received and all four diodes are nonconductive. The diodes remain nonconductive for about 4.3 seconds (258 input pulses). The AND output is connected to a two-stage transistor amplifier (not shown) whose output, generating the signal COUNT HOLD on line 50, is connected to the reset terminals of the first four stages of the counter 18. The first four counter stages are thus held in their OFF state for about 4.3 seconds at the end of the timing cycle, as shown in the timing diagram of FIG. 4. This action stops the counter 18 after 64 seconds of the timing cycle and prevents the counter from accumulating any further Geiger tube pulses during the following 4.3 seconds time period.

The PEN MOTOR ENABLE signal is generated within the timing logic unit 44 in similar fashion by diodes connected to stages 128, 256, 512, 1024 and 2048 of timer 38. An AND circuit output signal is developed only when 3868 input timer pulses (66.1 seconds) have been received and is maintained during the following 126 pulses (2.1 seconds). The AND circuit output is connected to the pen motor control circuit 48 for recorder 58. The recorder pen motor is thus disabled for 66.1 seconds, and then enabled for the following 2.1 seconds (see the timing chart of FIG. 4). The recorder, therefore, can only change its pen reading for 2.1 seconds at the end of the timing cycle when the counter 18 is stopped.

The COUNTER RESET signal is generated by the unit 44 in similar fashion by diodes connected to all 12 stages of the timer 38. An AND circuit output signal is developed only when all of the timer stages are ON. This occurs after 4095 pulses have been received, i.e., 17 milliseconds before the end of each timing cycle,'as shown in the timing diagram of FIG. 4. The output of the AND circuit is connected to the reset terminals of all but the first four stages of the counter 18, as noted above. The counter stages are thus turned to their OFF state just prior to the beginning of a new counting period.

The pen motor control circuit 48 is typically composed of a transistorized pen motor control module and a control relay (not shown). Input timing information for the pen motor control unit is obtained as the PEN MOTOR ENABLE signal on line 46 originating in the tinting logic unit 44. The pen motor control circuits allow the recorder 58 to record during the proper period in the timing cycle. When the signal appears on the line 46, the control relay is energized and the relay contacts (connected in a recorder pen motor reference winding) allow the motor to turn.

The recorder 58 (FIG. 2a) may be a conventional, round chart, 24-hour device, with a suitable pen motor control circuit. The recorder inputs are obtained on line 36 from the digital-toanalog converter 26 whose output is proportional to the coal bulk density, and on line 62 from an auxiliary logic and calibration assembly 60 (FIG. 2b). The input on the line 36 is divided through a span potentiometer (not shown) on the back of the recorder to provide a maximum of 50 millivolts, e.g., to a pen drive amplifier. Whenever an input signal occurs on line 62, the amplifier input is shorted (resulting in a recorder reading of 0). A signal is developed on line 62 when coal is not running to the hammermill, and the counter 30 does not indicate a normal" count, e.g., the 20th cycle, or the level of coal on the conveyor belt adjacent the radiation unit has not been maintained. This information is transmitted from the auxiliary logic and calibration assembly on line 62 and is derived, in turn, from a hammermill coal level paddle switch relay 63 (energized upon operation of the hammermill paddle switch 65, FIGS. 1 and 2b), a coal level relay 67 (energized by the coal level arm 33, FIGS. 1 and 3b), and the normal cycle output of cycle logic unit 56 by way of an amplifier 64.

The cycle logic unit 56 (FIG. 2b) is composed of AND circuits as in the tinting logic unit 44 described above. These circuits provide a NORMAL CYCLE signal and a LOW CYCLE signal. The inputs to the cycle logic unit are derived from the several cycle counter stages of cycle counter 30 and the last four stages of timer 38. The cycle logic unit 56 provides a NORMAL CYCLE signal to the auxiliary logic and calibration assembly 60 by way of an amplifier 64 when a predetermined counting cycle (e.g., the 20th cycle 1,310,720 to 1,375,232 Geiger tube pulses) has been obtained at the end of a timing cycle. The lack of this signal indicates an undesired bulk density, as explained below. In addition, the signal LOW CYCLE is transmitted to a low cycle integrator 66 by way of an amplifier 68 when another predetermined cycle (e.g., the 19th cycle 1,246,208 to 1,310,720 Geiger tube pulses) is obtained at the end of a tinting cycle.

The AND circuits within the cycle logic unit 56 function as follow s. The normal cycle AND circuit has as its inputs the I, 2, 4, 8 and 16 outputs of the cycle counter 30. The output of the corresponding AND circuit will provide an appropriate signal only when the fourth and 16th cycle counter stages are ON and the 1, 2 and 8 stages are OFF. This corresponds to the 20th cycle, which is representative and chosen only as an example. The inputs from the timer 38 (on lines 54) are from timer stages 256, 512, 1024 and 2048. The signals from these timer stages are acted upon in the unit 56 to provide a signal only during an appropriate time period (e. g., the last 4.3 seconds of the tinting cycle as represented by selected combinations of active signals on the lines 54). Therefore, the cycle logic unit 56 will genera te a normal cycle output signal only when the correct cycle (I, 2, 4, 8, 16) is obtained at the correct time (last 4.3 seconds) in the timing cycle. Without this output signal, the recorder pen and oil output will go to zero.

To explain further, the cycle counter 30 generates an output signal representing the number of Geiger tube pulses that have been generated by the Geiger tubes during the current timing cycle. If at the end of the timing cycle (the last 4.3 seconds) a count of 20 is indicated by the counter 30, a so-called normal" bulk density is indicated. As explained in connection with FIG. 5, the 20th counting cycle may represent a bulk density of from 43 to 53 pounds per cubic foot. A greater count than 20 from the counter 30 indicates a lesser bulk density (e.g., less than 43 pcf), and a lesser count indicates a greater bulk density (e.g., greater than 53 pcf). The count of 20 from the counter 30 has been selected as representing an appropriate bulk density range; one which is desired for a particular installation. Any count from the counter 30 may be taken as desired and is established by selecting appropriate ones of the outputs from the counter for application to the cycle logic unit 56.

The inputs to the 12w cycle part of the cycle logic unit 56 are from the l, 2, Z, 8, and 16 stages of cycle counter 30 (indicating a cycle count of 19, chosen by way of example) as well as the outputs of the timer 38 on lines 54. The unit 56 will generate a low cycle output signal only when the 19th cycle is obtained at the predetermined time in the timing cycle (e.g., the last 4.3 seconds). This condition will normally occur only when the coal density is between 53 and 65 pounds per cubic foot, for example. The output of the low cycle circuit is used in the water control system, as to be explained below, to initiate the application of maximum water to the coal.

To explain further, the low cycle part of the cycle logic unit 56 functions in the same manner as the normal cycle part of the circuit as described above. In particular, at the end of a timing cycle (e.g., the last 4.3 seconds), a low count from the counter 30 (e.g., a count of 19) indicates a relatively high bulk density, since few pulses have been generated by the Geiger tubes as counted in the counter 30. Any predetermined count within the counter 30 may be taken as a low cycle count to generate an appropriate output signal from the cycle logic unit 56 representing a relatively high bulk density, e.g., between 53 and 65 pounds per cubic foot.

The low cycle integrator 66 is composed typically of an RC time constant circuit (not shown). The input, as stated, is derived from the cycle logic unit 56, through the amplifier 68, and the output of the low cycle integrator operates a relay RL-C in the water control system (FIG. 3a), as to be further explained. The purpose of the integrator is to provide a time control signal to the water controller when the counter output is in the 19th cycle (indicating too high a bulk density). The controller, in turn, increases water output. The low cycle integrator is energized during each timing cycle (during the last 4.3 seconds) if there is an output signal from the cycle logic unit 56 indicating a cycle count of 19. Typically, one side of the RC circuit of the integrator 66 is connected to a DC supply, the other side is connected to ground through a transistor switch (not shown) in the cycle logic unit 56. The switch closes only when the 19th cycle is obtained during the correct time of the timing cycle (last 4.3 seconds). The switch closure applies power to the RC circuit, which includes the control relay RL-SC. The RC time delay holds the relay energized until another complete timing cycle has passed. If the counting cycle is again the 19th the RC circuit is reenergized. If the counting cycle is not the 19th the RC voltage decay will cause the relay to deenergize.

The auxiliary logic and calibration assembly 60 is composed of a normal cycle integrator and relay (not shown, like the low cycle integrator 66). The assembly is connected to a coal level relay 67, a hammermill paddle switch relay 63 and the amplifier 64. The inputs to the circuit are the signals NORMAL CYCLE on line 70, by way of the amplifier 64, the signal derived from the contact closure of the coal level switch 33 associated with the conveyor in series with the hammermill paddle switch relay contacts. The circuit provides an output to the recorder 58. The loss of coal level either at the hammermill or at the gage (radiation unit), as indicated by operation of the hammermill paddle switch 65 or the coal level arm 33, or the existence of a cycle other than the normal" cycle (as indicated by the absence of a normal cycle signal) will short the recorder input and reduce the oil control valve input to zero. The result is a zero recorder reading. The oil supply to the coal is also cut-off, as will be explained below.

The normal cycle integrator circuit functions exactly like the low cycle integrator except that an appropriate relay (not shown) is energized only if the th cycle is counted in the last 4.3 seconds of the timing cycle. The relay contacts are in series with a relay coil RL-3 (FIG. 3a) which has its circuit completed to ground only when the gage and hammermill coal levels are normal. With relay RL-3 energized, the recorder input short is removed, allowing the recorder to record. In addition, the contacts of RL-3 are closed, permitting oil valve 29 to be automatically controlled, as explained below.

The calibration circuits within the auxiliary logic and calibration assembly 60 are composed of a 15-minute timer motor/cam switch assembly, two relays, and a calibration switch (not shown). This latter circuit allows the recorder to record when coal is not running for the purpose of calibrating the system.

FIGS. 3a AND 3b The equipment used in the automatic control of oil and water additions to the coal at the hammermill is shown in FIGS. 3a and 31:. Primary bulk density control is achieved by automatically controlling the oil addition to the coal. A bulk density increase of 510 pounds per cubic foot can be achieved with as little as 0.3 gallon of oil per ton of coal. Secondary bulk density control is achieved by automatically controlling the water additions. Since water will reduce the coal bulk density, the objectives of the water control system are two-fold: to control the coal density when it is higher than the optimum and no oil is being added, and to provide good control without using excessive oil. Special equipment is provided to improve start-up control, resulting in faster attainment of a control set point with a minimum of overshooting.

In considering the following description, reference should be made to Table A (above) functionally summarizing system operation.

Automatic oil control is accomplished by using an oil controller 76 (FIG. 3b) at an oil selector station 78 which is capable of transmitting gain control and integral control signals. The controller input is obtained from the recorder 58 (FIG. 3a). The controller output operates the pneumatic oil control valve 29 at the hammermill (FIG. 3b). A pneumatic transmitter 84 (such as a Class PA, PB and PC pneumatic transmitter made by Bailey Meter Company of Wickliffe, Ohio) in the recorder (FIG. 3a) is mechanically linked to the recorder pen 86 and provides an air signal of from 3-15 pounds per square inch, for example, directly proportional to the pen position and thus bulk density. As an example, at 0 percent pen readinG (43 pcf bulk density) air output is 3 pounds per square inch. At percent pen reading (53 pcf bulk density) air output is 15 pounds per square inch. The transmitter output provides an input signal to a conventional oil controller 76, such as a type AD pneumatic controller made by Bailey Meter Company.

The oil controller 76 typically is a conventional pneumatic, three-mode device, providing gain (proportional), integral (reset) and differential (rate) control. The controller receives its input signal from the pneumatic transmitter 84, and a SET POINT signal from an adjustable selector 88 in the oil selector station 78. Any difference is operated upon in the controller 76 and produces an output pressure to operate the oil control valve 29 to eliminate the difference.

The oil controller 76, as stated, typically has three distinct control action adjustments, namely, gain control, integral control and derivative control. The latter control is, however, not used in the present gaging and control system due to the gaging technique employed.

Gain control is the inverse of the more commonly used proportional band control. Gain is defined as the change in controller output pressure divided by the change in input pressure. For example, with a gain setting of 0.5, a recorder pen position change of 10 percent produces a controller input pressure change of 0.1 X l2( 1 53=l.2 PSI. Controller output pressure change equals Gain X Change in input, or 0.5 X 1.2 0.6 PSI.

The oil selector station 78 provides a complete set of controls for manual or automatic oil control. Control of oil valve 29 is by pneumatic pressure applied to the valve (through solenoid 3) from the oil selector station. In addition, it provides a number of indicating meters to monitor the control process. The controls on the face of the oil selector station provide for manual or automatic oil selection, set point adjustment, manual oil adjustment, and bumpless hand-to-automatic transfer. In other words, transfer from manual to automatic operation produces no abrupt change in oil control valve setting. The four indicating meters on the front panel provide the following: the meter 90 indicates input pressure to the controller. During normal automatic control, this meter will indicate the output pressure from the recorder transmitter 84 which is directly proportional to the recorded bulk density. Between coal runs and at start-up, set-point pressure is fed to the controller input and is displayed on the meter scale which is calibrated in pounds per cubic foot.

The set point is selected by adjusting a set-point knob 97. The set-point scale 88 indicates at all times the set point bulk density which is selected. In automatic control, any difierence between the reading of the meter 90 and the setting of the setpoint control indicator 88 produces an output signal from the controller 76 to change the position of oil control valve 29. The indicator 92 indicates the percentage of maximum controller output pressure which is being employed. During normal automatic control, a percent reading indicates that the oil control valve is closed (3 PSI or less). A 100 percent reading indicates that the valve is completely open PSI or greater). Should a loss of coal level or incorrect cycle occur, a pair of solenoids 94 and 95 in the output lines of the oil and water control valves will close which, in turn, will cut ofi the flow of oil and water. Controller output pressure will still be displayed on the indicator 92. With the hand/auto switch 96 on automatic, the meter 90 indicates the position or setting of the oil valve 29 that would result if the control were switched to manual by reversing the switch 96. The meter reading can be adjusted with a manual oil addition control knob 93. In order to transfer from automatic to manual oil control during a coal run, without changing the existing position of the oil control valve 29 (to render the change bumpless, i.e., no abrupt changes in oil valve settings), the transfer meter reading is adjusted to equal the control meter reading by adjustment of control 93. When the Man/Auto switch 96 is then changed to manual, no change in the position of oil valve 29 will occur. In order to transfer from manual to automatic oil control during a coal run, the switch 96 is simply turned to Auto, because of the bumpless feature of the controller 78.

Four solenoid valves SOL. l, SOL. 2 (FIG. 3a), SOL. 3 and SOL. 4 (FIG. 2b) are used in the oil control system for the purpose of allowing a faster, smoother oil control at start-up and for reasons of safety.

Solenoid valve SOL. 1 is located in the air line which connects the set-point pressure to the signal input of the oil controller 76. During a normal, automatically controlled coal run, this valve is closed. If either coal level or the normal" (th cycle is lost during any timing cycle, the valve opens (as explained below) to provide a set-point pressure at the controller input. Since the oil controller 76 operates on the difference between the input pressure and the set-point pressure, and no difference occurs under this condition, the output from the oil controller 76 to the oil control valve 29 is held constant.

Solenoid valve SOL. 2 is located in the air line which connects the recorder transmitter 84 to the input of the oil controller 76. During a normal, automatically controlled coal run, the valve is open. If coal level or correct cycle is lost, the solenoid valve SOL. 2 closes (as explained below), preventing transmitter output pressure from reaching the input of the oil controller 76.

Solenoid valve SOL. 3 is located in the air line which connects the output of the oil controller 76 (through the oil selector station) to the oil control valve 29. This solenoid is open only when normal coal level and the correct cycle have been achieved (as explained below). It has been provided as a safety feature. A loss of coal level or the occurrence of an incorrect cycle, causes the oil control valve at the hammermill to close.

Solenoid valve SOL. 4 connects the oil selector station output pressure to the controller tieback connection. It is normally closed, opening only when coal level or cycle logic is lost, as explained below. This valve has been provided to assist in holding output pressure constant between coal runs.

The solenoid valves and their associated relays function as follows: When coal level at the hammermill switch 65 or coal level arm 33, or when the normal" cycle 20th) is lost, relay RL-3 (FIG. 3a) controlled by the auxiliary logic and calibration assembly 60 is deenergized. The resultant contact opening removes power from the solenoid valve SOL. 3, causing the oil valve 29 to close (FIG. 3b). In this regard, the valve SOL. 3 is arranged to vent the line leading to the oil control valve 29 when SOL. 3 is deenergized. Venting of the line causes the oil valve to close. The opening of the contacts of relay RL-3 also immediately deenergizes relay RL-lC FIG. 3a), removing power from the solenoid valves SOL. l, SOL. 2 and SOL. 4, thereby holding the oil controller output constant. This, in effect, provides a memory for the oil addition at the start of the next coal run.

It will be noted that the relay RL-3 has an additional set of contacts RL-3X which are closed when the relay is energized. When the contacts are closed, which occurs when the coal level is normal and when the cycle logic unit 56 is counting in the non-rial or 20th cycle, power is provided from the supply voltage source 116 to energize a solenoid valve SOL. 3X in the line leading from an electro-pneumatic converter 112 to the water valve 27. The energized solenoid valve SOL. 3X permits the water valve to be controlled by the converter 112. Control of the water valve by the converter will be explained in detail below. If the cycle logic unit 56 is not counting in the normal or 20th cycle, however, but is counting in the low" or 19th cycle (indicating a relatively high bulk density), the relay RL-3 will be deenergized. This would normally deenergize the solenoid valve SOL. 3X because of the opening of the relay contacts RL-SX. However, when the cycle logic unit 56 is counting in the 19th cycle, a signal is developed from low cycle integrator 66 which energizes the relay RL-SC. This relay includes a set of contacts RL-SCX which are closed when the relay is energized. These closed relay contacts connect the supply voltage source 116 to the solenoid valve SOL. 3X to energize the solenoid valve, thereby to continue to permit the water valve 27 to be controlled by the converter 112 even though the oil valve 29 is closed.

At the start of the next coal run, when normal coal level and the correct cycle have been achieved, relay RL-3 (FIG. 3a) is energized. This immediately applies power to the solenoid valve SOL. 3 and to the relay RL-lC (FIG. 3a), which is typically a time delay relay, having a 4 minute delay on pull-in, for example. The solenoid valves SOL. I, SOL. 2 and SOL. 4 are thus energized 4 minutes after the relay RL1C is energized (when the relay contacts close applying power to the solenoids). Thus, at the start of the coal run, the oil valve 29 is immediately returned to the position it occupied at the end of the previous run (by air pressure through SOL. 3 to the oil valve). This position is maintained for four minutes, after which normal automatic oil control is resumed when the solenoids SOL. l, SOL. 2 and SOL. 4 are energized.

An oil flow rate meter (FIG. 3a) receives its electrical input signal from a pressure to current transducer 100a (FIG. 1).

The water control system provides water additions in steps of 0 percent, 33 percent 66 percent and 100 percent of maximum available water-flow rate. The system consists of high and low bulk density cams 102 and 104 (FIG. 3a) and associated high and low oil addition limit switches 106 and 108 in the oil flow rate meter 100 (FIG. 3a), a number of control relays, including two adjustable time delay relays, a water controller circuit 110, the low-cycle integrator 66, and an electropneumatic converter 122, all of which will be described in greater detail in the following.

Switches S5 and S6 (FIG. 3a) which are operated respectively by the cams 102 and 104 provide means for initiating a change in the water addition rate. The cams 102 and 104, which are adjustable, are located on the shaft of the pen drive motor 114 and are preferably set to provide actuation of switches S5 and S6, respectively, at 1.5 pounds per cubic foot above and 2.0 pounds per cubic foot below the bulk density set point, for example. As can be seen by reference to FIG. 3a, when the bulk density falls outside of these limits, a signal from supply voltage source 1 16 is aPplied to either the water increase or to the water decrease" contacts 118, or 120, respectively, of the relay RL-4C. Note that a low bulk density condition will impress a signal on the water decrease contacts 120, while a high bulk density will produce a signal at the water increase contacts 1 18.

The contacts 106 and 108 of the oil flow rate meter 100, which are adjustable, are directly connected to and are driven by the pointer 101 of the meter. The contacts 108 will close when the rate of oil addition falls below a minimum value selected by the operator. The contacts 106 will close when the rate of oil addition becomes excessive. Closure of either set of contacts 106 or 108 will transmit a water corrective signal to the appropriate contacts of relay RL-4C only if the bulk density is within a selected range. An inspection of FIG. 3a will show that the oil addition limit switches 106 and 108 are wired in series with the normal bulk density contacts of the bulk density cam switches S5 and S6. in this way, the oil addition limit switches 106 and 108 are only effective under normal bulk density conditions. To explain, a signal from supply voltage source 116 can only be applied to the limit switches 106 and 108 if both switches S5 and S6 are in the positions shown in FIG. 3a, i.e., in normal bulk density positions.

The control relay circuits function as follows:

When proper coal level and the correct counting cycle information is received, relay RL-3 (FIG. 3a) is energized. Energizing relay RL-3 applies power to the time delay RL-lC. A time delay of 4 minutes takes place before the contacts of relay RL-lC are closed. When so closed, these contacts apply power to energize the relay RL-4C and transfer any water corrective signal to the contacts of relay RL-6C or to the contacts of relay RL-7C, which are the decrease" and increase water gating relays, respectively. The control of relays RL-6C and RL-7C will be further explained below. Their purpose, it might be said at this point, is to disconnect the water controller circuitry from an increase" signal when maximum water is already being added to the coal, and from a decrease" signal when no water is being added.

An increase water signal transmitted through the contacts of relay RL-7C or a decrease" water signal transmitted through the closed contacts of relay RL-6C will be applied to the coil of a time delay relay RL2C (FIG. 3a). A time delay of 4 minutes, for example, takes place before the contacts of relay RL-ZC are opened. Such opening deenergizes the relay RL-9C, causing the contacts of the relay to close, and simultaneously interrupts the current to the coil of relay RL-2C, causing relay RL-2C to drop out (close its contacts and begin a new 4 minute timing cycle). Relay RL-9C is thus again energized. Relays RL-2C and RL-9C acting together supply a pulse input signal to the water controller 110 (by the momentary closing of the contacts of relay RL-9C) to effect a change in water level, while relay RL-8C instructs the water controller as to the direction of change, i.e. whether water is to be increased of whether water is to be decreased. The relay RL-8C is energized with a decrease water signal, which causes the water controller 110 to count backwardly; relay RL-8C remains deenergized when an increase water signal occurs, which causes the water controller 110 to count forwardly. (Note the connections shown on the water controller 110 in FIG. 3a and the contacts of relay RL8C.) The water controller 110 is a conventional forward-backward counter typically formed from two bistable multivibrators (not shown). The two multivibrators provide four possible output signals (neither multivibrator conducting, a first conducting and the second nonconducting, or vice-versa, and both conducting) represented by different voltage levels of output connections 1 and 2 of the water controller. The contacts of relay RL-8C reverse connections of the multivibrators so as to reverse the sequence of output signal changes for successive input pulses.

Due to the time delay of relay RL-2C and its self-interrupting contacts, water corrections cannot be made any, more frequently than once every 4 minutes. The delay ensures that control oscillations will not occur, since sufficient time is allowed to elapse for the system to respond to a change in water addition rate before another change can be made.

Another way to effect a change in the level of water addition is by means of a relay RL-SC (FIG. 3a) which receives its signals from the low cycle integrator 66 (FIG. 2b). In FIG. 3a, it can be seen that closure of the contacts of relay RL-SC due to extremely high bulk densities (19th cycle) will increase the rate of water addition, since contact closure applies a signal to the "increase" water contacts RL-7C.

The water controlling system includes the water controller 110, an amplifier 122, a counts-to-current converter circuit 124 (FIG. 3b) and a gating circuit 126. As noted above, a pulse at the count input terminals of the water controller,

produced by momentary closure of the contacts of relay RL-9C, causes the unit to count either forwardly or backwardly, particularly depending upon the state of the relay RL-SC. The output terminals 1 and 2 of the water controller provide a6 V. or a 0 V. signal, for example. Negative 6 V. at either output signifies an ON condition for that particular multivibrator stage. The counter outputs are applied to the amplifier 122 and also to the gating circuit 126.

The amplifier 122 couples the water controller outputs to the counts-to-current converter circuit 124 and to a set of water addition indicator lamps L6 and L7. The lamps indicate directly the state of both of the water controller multivibrator stages, and the level of the water addition. When neither lamp is energized, 0 percent water addition is indicated. When lamp L6 is energized, it indicates a 33 percent water addition. When lamp L7 is energized, it indicates a 66 percent addition, and when both lamps are energized, a percent water addition is indicated.

The counts to current converter circuit 124 is a circuit for converting the digital output from the water controller to a series of current outputs. These output currents are applied to the electro-pneumatic converter 112 to operate the water control valve 27 (FIG. 3b). Basically, the count to current converter 124 consists of three switchable voltage sources (not shown), ranging from 4 to 8.2 volts, for example. These sources are switched on and off by means of the output of the water controller 110 after amplification by the amplifier 122. The water controller outputs are fed into an AND circuit (not shown) which selects the largest available output. The source voltages are chosen such that an ON output 1, an ON output 2 and both outputs 1 and 2 ON from the water controller provide currents into the electro-pneumatic converter 112 of about 2.6 ma., 3.5 ma., and 5.5 ma., respectively, for example. The currents 2.6 ma., 3.5 ma. and 5.5 ma. to the converter 112 cause the water valve 27 to be 33 percent open, 66 percent open and 100 percent open, respectively, for example.

The gating circuit 126 consists of two parallel AND gates (not shown) of two inputs each. These gates control the coils of relays RL-6C and RL-7C to disconnect the input of the water controller 110 from the water correction signals when further correction in the direction indicated by the signals from the gating circuit would be impossible. For example, ON outputs 1 and 2 from the water controller (maximum water addition) will cause the gating circuit 126 to deenergize the relay RL-7C, which is otherwise energized, and open the relay contacts. This disconnects the water controller 110 from any increase" water signal. Likewise, zero outputs at the 1 and 2 output terminAls of the controller 110 (no water needed) will cause the relay RL-6C to become deenergized, opening the relay contacts and disconnecting any decrease" water signal from the counter.

The electro-pneumatic converter 112 is a conventional Leeds & Northrop electro-pneumatic converter, for example. It provides 3-15 PSI air, for example, to position the water control valve 27. Its electrical input is a l to 5.5 ma. DC current, for example, obtained from the output of the counts to current converter circuit 124, as explained above.

PLOW DESIGN As noted above, the design of the plow 19 (FIG. 1), which carries the radiation source 21, is particularly important to ensure that the coal or other granular material is properly handled for a correct determination of bulk density. The plow is shown in detail in FIGS. 6 and 8, and includes a frOnt wedgeshaped portion 19a facing in the direction from which the granular material is supplied. The wedgeshaped front portion terminates in a forwardly extending prow 19b. The prow 19b essentially consists of a plate curved from upper part 19c of the forward end of theprow to lower part 19d of the rearward end of the prow. As granular material is applied to the plow, the material is divided by the prow 19b and the wedge-shaped forward plow portion 19a so that it passes smoothly to both sides of the plow. The curved part of the prow permits the material to pass easily underneath the plow so that radiation may pass downwardly through the materiaL'It will be noted then that the plow serves the purpose of isolating a part of the granular stream of material which is of uniform thickness, i.e. in a dimension downwardly from the plow. The thickness is determined by the distance of the plow above the conveyor conveying the granular material (distance d in FIG. 8). It has been found that the curved prow 19b and the wedge-shaped plow portion 19a engage and properly direct the granular material without afiecting the bulk density of the material by this action. Thus the plow permits accurate gaging of the material. AdditionAlly, the design of the plow prevents foreign matter such as wire and the like from becoming caught on the plow.

FIGS. 6a and 6b show the interior of the plow 19 and container 31, illustrating the details of the mounting of the radioactive source 21. As shown in FIG. 6b, the radioactive source is carried on the end of a threaded rod 170 positioned inside a threaded tube 170a. The rod 170 is connected to a gear 172 driven by a worm 174 shown in FIG. 6a. The worm 174 is in turn driven by a motor 176. The motor is energized selectively to drive the worm 174 so as to raise and lower the radiation source 21 to a suitable position within the interior of the plow. The position of the radiation source determines the efiective amount of granular material irradiated by the source, as will now be explained.

Lead or other shielding 178 is utilized within the plow 19 to contain the radiation from the source 21. A bottom piece 178a of the shielding is movable as shown by the arrows to the position shown in dashed lines. In the dashed line position of the bottom piece, radiation can pass downwardly from the source 21 through bottom plate l9e of the plow 19. Typically, the bottom plate 19e is of steel which does not deter the radiation from passing therethrough. The radiation source 21 is thus completely enclosed by lead shielding except therebelow following the positioning of the shielding piece 178a to the left of FIG. 6b. The opening in the shielding so provided acts as an effective lens to determine the divergence of the radiation beam from the source 21. Dashed lines 180a and 180b represent the effective maximum divergence of rays of energy from the source 21. The dashed lines are determined by drawing lines in FIG. 6b from the source 21 to the inside edges of the shielding at the opening provided by the block 178a moved to the left. It will be appreciated that, as the radiation source 21 is lowered, the radiation becomes more divergent as it passes through the bottom plate 192; as the radiation source 21 is raised, the radiation becomes less divergent. Thus by controlling the position of the radiation source within the plow 19, the radiation can be made to irradiate a larger or a lesser portion of granular material, as desired.

Typically, the opening for radiation to pass through the bottom plate 19e of the plow (provided for by moving the block 178a to the left) is rectangular in shape. Any shape radiation opening can be provided in the shielding as desired for the purpose of irradiating the granular material. In any event, a uniform volume of material is irradiated once the position of the plow 19 is fixed above the conveyor 15 (determining the distance d in FIG. 8), and the radiation source 21 is adjusted within the plow 19. For the purpose of calibration, it may be desirable periodically to insert a calibration plate (not shown) typically of lead and steel beneath the plow 19. The plate serves to simulate a quantity of granular material of standard bulk density. With the plate in position, the recorder pen 86 of the bulk density recorder shown in FIG. 3a should provide a particular indication corresponding to the standard bulk density simulated by the plate. If such an indication is not obtained, suitable adjustment of the radiation source 21 may be made until the correct indication is obtained.

SIMULATING THE FALL OF COAL IN A COKE OVEN As explained above, the conveyor 13 is adjustable in height over the conveyor 15 (FIG. 1) so as to provide a drop of coal just prior to the determination of bulk density that simulates the drop in an oven. In this fashion, the coal is provided to the radiation source in a bulk density condition the same as that existing in the oven. This procedure is necessary to ensure correct bulk density control. Oftentimes it is impossible, however, to provide a drop the same as that in a coke oven, since the drop might be too great for a conveying system at a particular mill. The present invention contemplates two drop simulating techniques. Apparatus for carrying out the first type of simulation is shown in FIGS. 6 to 8 and comprises a sled assembly formed from a plurality of individual sleds 152. Six of such sleds are shown positioned across the conveyor 15, although this number is arbitrary. Each sled is carried by rods I54 pivotally secured thereto. The rods 154 are pivotally sup ported by support members 156 extending across and over the conveyor. The sleds 152 may have weights 158 positioned thereon. As shown in FIG. 7, the heights of the sleds 152 above the conveyor 15 may vary so that, in efiect, the sled assembly assumes a general arcuate shape over the conveyor as viewed in a direction in line with the movement of the granular material on the conveyor.

The sled assembly as carried in the support members 156 is free to pivot in an are generally in line with the movement of the granular material on the conveyor (see FIG. 8). The individual sleds of the sled assembly pivot in arcs and, in their engagement with the coal, cause the bulk density to be changed to simulate the drop of the coal in the coke ovens and the accompanying change in bulk density that takes place there.

An alternative scheme is shown in FIG. 9 in which a conveyor 160 conveys coal which is dropped to conveyor 15 takes the material to the plow 19. In this case the drop between the conveyors 160 and 15 is not the same as the drop in the ovens to which the material is supplied. Accordingly, a paddle-wheel assembly 162 is positioned between the conveyors driven by a motor 164 under control of a motor speed control 166. The paddle-wheel assembly rotates, as shown by the arrow in FIG. 9, and blades 162a of the assembly strike the coal as it falls from the conveyor 160 onto the conveyor 15. The speed of rotation of the paddle-wheel assembly and the impact provided to the falling coal by the paddle-wheel blades is varied until the appropriate simulation of the bulk density change produced by the drop at the coke ovens is achieved.

SUMMARY It can be seen from the foregoing that a precision gaging system has been provided notwithstanding the use of simple and relatively inexpensive, rugged and highly reliable Geiger Muller tubes, which are particularly adapted to the severe environment of a coke plant. Radiation pulse counting during each successive counting cycles provides an averaging of the signal nullifying the efiects of random variations.

Moreover, it can be appreciated that the unique system of increasing and decreasing water in fixed increments provides a precise degree of control. Oil and water control is achieved when the bulk density is within a predetermined range (19th and 20th cycles). If too high a bulk density is encountered within this range (19th cycle), oil is discontinued and water is increased. Water is also varied dependent upon the oil rate so as to achieve optimum oil addition conditions. Ifextreme bulk density conditions occur (below 19th cycle or above 20th cycle) oil and water are discontinued. Coal levels are monitored to cease oil or water and oil flows if levels are not maintained.

Finally, the electro-pneumatic solenoid system, which is embodied, provides, in effect, a memory for the controller to facilitate normal operations, without delay, upon resumption of operation after a shutdown. The coal handling process does not normally run continuously. Frequent shutdowns occur due to plugged chutes, or irregular coal feed, etc. Normally, it takes a considerable amount of time to bring the controlled bulk density back to the required set point after start-up.

These delays have been eliminated by the system herein by the fact that the control valve positions existing during normal operation are maintained at shutdown. Thus, upon resumption of operations, the liquid additions to the coal are the same that prevailed at shutdown. Following a short delay, at start-up to allow the bulk density of the coal to stabilize, the control circuit is switched back to the normal control mode of operation. Very little time is, therefore, required after start-up to reach and hold the required bulk density set point.

It should be noted that the control system operates in a series of successive timing cycles. In the embodiment disclosed each cycle is 64 seconds. At the end of each cycle, the radiation pulse count is determined and control signals are developed for varying oil and/or water addition rates. Although the timing cycle is 64 seconds, water is changeable only once every 4 minutes, an arbitrary period chosen to avoid system oscillation. Oil flow rate changes are not so restricted since the control provided by the oil controller is slowly changeable to avoid such oscillation.

While the novel features of the invention has been illustrated and described in connection with presently preferred embodiments, it is evident that these embodiments will enable others skilled in the art to apply the principles of the invention in forms departing from exemplary embodiments herein, and such departures are contemplated by the claims.

We claim:

1. In a system for regulating the bulk density of a granular material by the addition of fluid oil and water to the material, and including means for monitoring the bulk density of the material comprising a radiation source for directing radiation to the material and means for detecting radiation from the material, and means for monitoring the rate of addition of a first one of said fluids to the material, the improvement comprising means jointly responsive to said monitored bulk density and to said monitored fluid addition rate for regulating the addition of the other of said fluids to the material to control bulk density, said regulating means including means for varying the rate of addition of said other of said fluids when the rate of addition of said first fluid is outside a given range.

2. A system as defined in claim 1, wherein said bulk density monitoring means comprises means in response to radiation directed to the material for generating a pulse signal, the pulse repetition rate of which is representative of said bulk density, and means for counting the pulses of the pulse signal for a predetermined time, said counting means being periodically reset so as to count pulses of the pulse signal in successive counting cycles.

3. A system as defined in claim 1, wherein the regulating means includes means for varying the rate of addition of the first one of said fluids in accordance with said monitored bulk densit 4. X system as defined in claim 1, wherein the regulating means controls the addition of water in accordance with the oil addition rate.

5. A system as defined in claim 4, wherein the regulating means controls the addition of water by: (a) decreasing the rate of water addition if the rate of oil addition exceeds an upper limit, and (b) increasing the rate of water addition if the rate of oil addition is below a lower limit.

6. A system as defined in claim 1, wherein the regulating means controls the addition of oil and water by discontinuing all water and oil addition if the monitored bulk density is outside a predetermined range.

7. A system as defined in claim 1, wherein the regulating means discontinues oil addition if the monitored bulk density is outside a preestablished range.

8. A system as defined in claim 7, wherein the regulating means increases the rate of water addition if the monitored bulk density is higher than the bulk densities in the preestablished range.

9. A system as defined in claim 8, wherein said rate of water addition is increased until a maximum water addition rate is achieved or the monitored bulk density returns to said preestablished range within a predetermined time.

10. A system as defined in claim 1, wherein the means for directing radiation to the material includes means for providing radiation of a predetermined portion of the material.

11. A system as defined in claim 10, wherein the means for directing radiation to the material comprises a housing for containing the source of radiation, the housing being positioned above a conveying means which conveys granular material past the radiation source, the distance of the housing above the conveying means determining the thickness of the portion of granular material acted upon by the radiation, the housing including lead shielding to provide a beam of radiation outwardly from the housing, the position of the radiation source within the housing and the extent of the shielding determining the shape of the beam and hence the extent of the portion of material irradiated by the radiation.

12. A system as defined in claim 11, including adjustable means mounting the radiation source within the housing at any of a plurality of positions to control the extent of the portion of material irradiated by the radiation.

13. A system as defined in claim 1, including means for discontinuing fluid addition to the granular material, and means for maintaining the rate of fluid addition to the granular material at the rate prior to discontinuance when the addition of fluid is again continued.

14. A system as defined in claim I, particularly adapted for the regulation of bulk density of coal supplied to a coke oven, wherein the detecting means comprises a plurality of Geiger- Muller tubes for generating the pulse signal reliably under extreme conditions such as temperature.

15. In a system for regulating the bulk density of a granular material by the addition of fluid oil and water to the material, and including means for monitoring the bulk density of the material comprising a radiation source for directing radiation to the material and means for detecting radiation from the material, and means for monitoring the rate of addition of a first one of said fluids to the material, the improvement comprising regulating means for effecting primary control of bulk density by variation of the rate of addition of said first fluid in accordance with said monitored bulk density, said regulating means including means for varying the rate of addition of said other of said fluids only when said monitored rate of addition of said first fluid is outside a given range.

Claims (15)

1. In a system for regulating the bulk density of a granular material by the addition of fluid oil and water to the material, and including means for monitoring the bulk density of the material comprising a radiation source for directing radiation to the material and means for detecting radiation from the material, and means for monitoring the rate of addition of a first one of said fluids to the material, the improvement comprisiNg means jointly responsive to said monitored bulk density and to said monitored fluid addition rate for regulating the addition of the other of said fluids to the material to control bulk density, said regulating means including means for varying the rate of addition of said other of said fluids when the rate of addition of said first fluid is outside a given range.

2. A system as defined in claim 1, wherein said bulk density monitoring means comprises means in response to radiation directed to the material for generating a pulse signal, the pulse repetition rate of which is representative of said bulk density, and means for counting the pulses of the pulse signal for a predetermined time, said counting means being periodically reset so as to count pulses of the pulse signal in successive counting cycles.

3. A system as defined in claim 1, wherein the regulating means includes means for varying the rate of addition of the first one of said fluids in accordance with said monitored bulk density.

4. A system as defined in claim 1, wherein the regulating means controls the addition of water in accordance with the oil addition rate.

5. A system as defined in claim 4, wherein the regulating means controls the addition of water by: (a) decreasing the rate of water addition if the rate of oil addition exceeds an upper limit, and (b) increasing the rate of water addition if the rate of oil addition is below a lower limit.

6. A system as defined in claim 1, wherein the regulating means controls the addition of oil and water by discontinuing all water and oil addition if the monitored bulk density is outside a predetermined range.

7. A system as defined in claim 1, wherein the regulating means discontinues oil addition if the monitored bulk density is outside a preestablished range.

8. A system as defined in claim 7, wherein the regulating means increases the rate of water addition if the monitored bulk density is higher than the bulk densities in the pre-established range.

9. A system as defined in claim 8, wherein said rate of water addition is increased until a maximum water addition rate is achieved or the monitored bulk density returns to said preestablished range within a predetermined time.

10. A system as defined in claim 1, wherein the means for directing radiation to the material includes means for providing radiation of a predetermined portion of the material.

11. A system as defined in claim 10, wherein the means for directing radiation to the material comprises a housing for containing the source of radiation, the housing being positioned above a conveying means which conveys granular material past the radiation source, the distance of the housing above the conveying means determining the thickness of the portion of granular material acted upon by the radiation, the housing including lead shielding to provide a beam of radiation outwardly from the housing, the position of the radiation source within the housing and the extent of the shielding determining the shape of the beam and hence the extent of the portion of material irradiated by the radiation.

12. A system as defined in claim 11, including adjustable means mounting the radiation source within the housing at any of a plurality of positions to control the extent of the portion of material irradiated by the radiation.

13. A system as defined in claim 1, including means for discontinuing fluid addition to the granular material, and means for maintaining the rate of fluid addition to the granular material at the rate prior to discontinuance when the addition of fluid is again continued.

14. A system as defined in claim 1, particularly adapted for the regulation of bulk density of coal supplied to a coke oven, wherein the detecting means comprises a plurality of Geiger-Muller tubes for generating the pulse signal reliably under extreme conditions such as temperature.

15. In a system for regulating the bulk density of a granular material by the addition of fluid oil and water to the material, and including means for monitoring the bulk density of the material comprising a radiation source for directing radiation to the material and means for detecting radiation from the material, and means for monitoring the rate of addition of a first one of said fluids to the material, the improvement comprising regulating means for effecting primary control of bulk density by variation of the rate of addition of said first fluid in accordance with said monitored bulk density, said regulating means including means for varying the rate of addition of said other of said fluids only when said monitored rate of addition of said first fluid is outside a given range.

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