US3891366A - Pelleting of carbon black - Google Patents

Abstract

Carbon black is formed into pellets by introducing carbon black and a pelletizing fluid into a pellet mill which contains a mixing device. The mixing device is driven by a motor which is connected to the device by a variable speed transmission. The flow of pelletizing fluid into the mill is controlled in response to a measurement of the power consumed by the motor. A measurement is made of the density of carbon black pellets removed from the mill. In response to this density measurement, the variable speed transmission is controlled so that pellets of uniform density are produced.

Description

1 1 June 24, 1975 1 1 PELLETING OF CARBON BLACK Wilson 11. Rushiord, London. England [75] Inventor:

[73] Assignee: Phillips Petroleum Company,

Bartlesville. Okla.

[22] Filed: Mar. 13, 1974 [2]] Appl. No.: 450,576

[52] US. Cl. 425/140; 425/222; 23/314; 259/3; 264/117 [51] Int. Cl. 8013' 2/12; CO9C 1/58 158] Field of Search H 23/314, 313; 425/222, 140; 259/3, 85; 264/117 I 56] References Cited UNITED STATES PATENTS 2.699.381 1/1965 King 23/314 2.800.399 7/1957 King 23/314 POWER SOURCE POWER MEASUREMENT 3,266,873 8/1966 Alleman 23/314 3.266.874 8/1966 Allcman 23/314 3,293.003 12/1966 .Iones 23/314 FOREIGN PATENTS OR APPLICATIONS 698,539 11/1964 Canada 23/314 845.041 8/1960 United Kingdom 23/314 952.220 3/1964 United Kingdom 23/314 Primary Examiner-Norman Yudkoff Assistant Examiner-S. .1. Emery [57] ABSTRACT Carbon black is formed into pellets by introducing carbon black and a pelletizing fluid into a pellet mill which contains a mixing device. The mixing device is driven by a motor which is connected to the device by a variable speed transmission. The flow of pelletizing fluid into the mill is controlled in response to a measurement of the power consumed by the motor. A measurement is made of the density of carbon black pellets removed from the mill. In response to this density measurement, the variable speed transmission is controlled so that pellets of uniform density are produced.

3 Claims, 1 Drawing Figure LK /PELLE'I'IZING FLUID PELLET MILL VARIABLE SPEED TRANSM l SSlON PELLETING OF CARBON BLACK Loose carbon black as produced has a very low density which makes it extremely difficult to handle and transport. For this reason, it is common practice in the industry to form the black into pellets which have a greater density than the loose black. This can be accomplished by the use of a pellet mill which contains a mixing device, such as a rotatable shaft having a plurality of pins extending therefrom. The loose black and an aqueous pelletizing liquid are introduced into the inlet of the mill, and pellets are withdrawn from the outlet of the mill. It is desirable that the pellets have a uniform bulk density in order to facilitate blending of the carbon black into rubber or other products.

In view of the fact that loose carbon black is inherently difficult to handle and process. it is often difficult to control pelleting operations to produce the desired uniform pellets. One control procedure which has been employed heretofore involves measuring the power consumed by the driving means connected to the mixing device. ln response to this measurement, the flow of pelletizing liquid into the mill is regulated so that substantially a constant amount of energy is imparted to the mixing device. While this procedure greatly improves pelleting operations. the bulk density of the produced pellets often is not completely uniform.

ln accorrdance with this invention, a carbon black pelleting operation is improved by measuring the bulk density of the pellets withdrawn from the pellet mill. In response to this measurement, the speed at which the mixing device is operated in the pellet mill is varied to provide pellets having a more uniform density.

The accompanying drawing is a schematic representation of carbon black pelleting apparatus having an embodiment of the control system of this invention incorporated therein.

Referring now to the drawing in detail, there is shown a conventional pellet mill 10 which comprises an elongated, generally cylindrical chamber having a mixing device positioned therein. This device can comprise a rotatable shaft 11 having a plurality of spaced pins 12 extending therefrom. Loose carbon black is passed from a storage vessel 13 through a conduit 14 to the inlet end of pellet mill 10. A control valve, such as a rotatable star valve 15, is disposed in conduit 14 so that the carbon black can be introduced at a relatively uniform rate. A pelletizing fluid. which normally comprises an aqueous liquid such as water or a mixture of water and molasses, is introduced into the inlet end of pellet mill through a conduit 16. The flow of fluid through conduit [6 is regulated by a flow controller 17 which adjusts a valve 18. Pellets are withdrawn from the outlet end of mill through a conduit 20 which communicates with the inlet ofa dryer 21. Dried pellets are removed through a conduit 22. The apparatus thus far described constitutes conventional carbon black pelleting and drying apparatus.

Shaft 11 of the mixing device is rotated by a motor 23 which is connected to a power source 24. The drive shaft of motor 23 is connected by a variable speed transmission 25 to shaft ll. Motor 23 is operated at a substantially constant speed. A power measuring element 26 measures the energy consumed by motor 23 and establishes an output control signal responsive thereto. This device can be connected by transformer 27 to one of the power leads to the motor to measure the current through this lead, for example. The output signal from element 26 is applied as the setpoint signal to flow controller 17. In this manner, the flow of pelletizing fluid is adjusted in response to variations of power consumed by the motor, which in turn are representative of variations in energy imparted to the mixing device in the pellet mill. The control of the flow of pelletizing fluid in this manner is known in the art, and is described in U.S. Pat. No. 3,249,263, for example.

While the foregoing control system improves the uniformity of the pellets produced, it is desirable to provide an even greater control of the bulk density of the pellets. This is accomplished in accordance with the present invention in response to a measurement of the bulk density of the produced pellets. To this end, a conduit 30 extends between conduit 20 and a density measuring device 31 to supply a sample of the produced pellets to the density measuring device. These pellets can be returned to conduit 20 through a conduit 32. Density measuring device 31 can be any one of the density measuring devices described in U.S. Pat. No. 3,807,523, for example. A tachometer 33 is connected to shaft 11 to establish a signal representative of the speed of rotation of the shaft. This signal is applied to the input of a conventional controller 34 which regulates variable speed transmission 25. The setpoint of controller 34 is adjusted by the output signal from density measuring and control device 31. In the absence of a change in the output signal from device 31, transducer 33 operates through controller 34 and transmission 25 to maintain a constant speed of rotation of shaft 11. If the measured bulk pellet density should change, the setpoint of controller 34 is adjusted so that the speed of rotation of shaft 11 is changed. It has been found that the bulk density of the produced carbon black pellets is increased when the speed of rotation of the mixing device is increased. In accordance with the invention, the speed is adjusted by variable speed transmission 25 so that pellets having a predetermined desired value of bulk density are produced. This requires the speed to be increased if the measured bulk density falls below a desired preselected value and decreased if the measured bulk density rises above such value. Variable speed transmission 25 can be a device of the type described in Marks Mechanical Engineers Handbook," McGraw-Hill Book Company, Inc., New York, I958, pages 10-52, for example.

This density control of the pellet mill is particularly effective when employed in combination with control of the rate of introduction of the pelletizing fluid in response to a measurement of the energy imparted to the mixing device. The two control elements operating together function to produce pellets of uniform bulk density.

As an example of a typical operation of the control method of this invention, pellet mill 10 can have a diameter of about 20 inches and a length of about 9 feet. Shaft 11 is rotated at a speed of about 320 revolutions per minute in normal operation. Carbon black, such as type N330, is introduced into mill 10 at a rate of about 1,750 pounds per hour. The pelletizing liquid is water containing about 0.5 to 1.0 weight percent molasses. This liquid is normally introduced into mill 10 at a rate of about 1,750 pounds per hour. The bulk density of loosely packed pellets produced in mill 10 is maintained at about 22 pounds per cubic foot. The calibration of controller 34 can readily be adjusted in a given operation from a measurement of the change in density which results from a given change in speed of shaft rotation. The control apparatus is then set to produce carbon black having a desired bulk density.

While this invention has been described in conjunction with a presently preferred embodiment, it should be evident that it is not limited thereto.

What is claimed is: 1. Apparatus for pelleting carbon black comprising: a generally horizontal pellet mill having a carbon black inlet, a pellet outlet, and axial rotary pin agitator mixing means positioned with said pellet mill;

conduit means communicating with said pellet mill to introduce a pelletizing liquid;

a motor;

a variable speed drive means connected said motor to said mixing means;

means to measure the bulk density of a volume of pellets removed from the outlet of said pellet mill and to establish a signal representative of the measured bulk density; and

means responsive to said signal to control said variable speed drive means to adjust the speed at which said mixing means is rotated in response to changes in the measured density said responsive means aetuating said mixing means at a lower rate of speed if the measured bulk density increases above a predetermined value and at a higher rate of speed if the measured bulk density decreases below said predetermined value.

2. The apparatus of claim 1. further comprising means to measure the power consumed by said motor and to establish a second signal representative thereof, and means responsive to said second signal to control the flow of pclletizing fluid through said conduit means.

3. The apparatus of claim 2 wherein said motor is an electric motor which operates at substantially a constant speed, and wherein said means to measure power consumed comprises means to establish a signal representative of current supplied to the motor.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,891,366

DATED 1 June 24, 1975 |NVENTOR(S) 3 Wilson H. Rushford It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 21, delete "3,807,523" and insert therefor Signed and Scaled this A ttesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufParenls and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,891,366

DATED 1 Jun 2TH 1975 INVENTOR(S) 1 Wilson H. Rushford tt is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 11, delete "with" and insert therefor within column 3, line 15, delete "connected" and insert therefor connecting [SEAL] Arrest:

RUTH C. MASON Arresting Officer Signed and Scaled this seventeenth D 3y Of February 1976 C. MARSHALL DANN Commissioner uj'larerrls and Tradvnwrks

Claims (3)

1. APPARATUS FOR PELLETING CARBON BLACK COMPRISING: A GENERALLY HORIZONTAL PELLET MILL HAVING A CARBON BLACK INLET, A PELLET OUTLET, AND AXIAL ROTARY PIN AGITATOR MIXING MEANS POSITIONED WITH SAID PELLET MILL; CONDUIT MEANS COMMUNICATING WITH SAID PELLET MILL TO INTRODUCE A PELLETIZING LIQUID; A MOTOR; A VARIABLE SPEED DRIVE MEANS CONNECTED SAID MOTOR TO SAID MIXING MEANS; MEANS TO MEASURE THE BULK DENSITY OF A VOLUME OF PELLETS REMOVED FROM THE OUTLET OF SAID PELLET MILL AND TO ESTABLISH A SIGNAL REPRESENTATIVE OF THE MEASURED BULK DENSITY; AND

2. The apparatus of claim 1, further comprising means to measure the power consumed by said motor and to establish a second signal representative thereof, and means responsive to said second signal to control the flow of pelletizing fluid through said conduit means.

3. The apparatus of claim 2 wherein said motor is an electric motor which operates at substantially a constant speed, and wherein said means to measure power consumed comprises means to establish a signal representative of current supplied to the motor.

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