US3482327A - Method and apparatus for controlling the drying rate in a wet pellet dryer - Google Patents

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9, 1969 D. l.. Du'TcHE-R 3,482,327 METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLET DRYER Filed March 22,` 1968 4 Sheets-Sheet l A 7' TORNEVS R m n m U W m2 m D @n mm v L. N l... mm( 5.30.5200 1 D mm o .m S @n n Nm ill Y, vm m B H v w mu zm2 da www NN mm. n m wm mbwllll oEA..I nim mm. ov QL a mx im u .m 10m UOM NvK. 55E @MN wm Al w .Bonomi l mm w v m nmjm t mmQ 5.3mm .A mmrwa w 5521.1. L m v w m Q sv vm. mm N. x93@ mm.\. v m.\. n .m WM. l l I I I I III! Il!! /Em zomm u .T s L, s Nm mv Dec. 9, 1969 D. L. 'DUTCHER 3,482,327

METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLET DRYER Flled March 22. 1968 4 Sheets-Sheet 3 LB/MIN SCF/MIN IOO WIJ

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|000 207 .F x u A A Deu.` 9, 1969 D, L. DUTCHER Y 3,482,327

METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLET DRYER Filed Mann 22, 1968 4 sheets-sheet 4 loo 30| 3H 3:2 LB/Mm A\........

2000 302 F l v zooo 303 SCF/MIN l L f-- INVENTOR.

D. L DUTCHER @www United States Patent() METHOD AND APPARATUS FOR CONTROLLING THE DRYING RATE IN A WET PELLET DRYER Dennis L. Dutcher, St. Louis, Mo., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Mar. 22, 1968, Ser. No. 715,360 Int. Cl. F26b 21/10, 7/00 U.S. Cl. 34-12 10 Claims ABSTRACT OF THE DISCLOSURE Carbon lblack and water are admixed in a pelletizer and passed to a pellet dryer. The ow rate of water to the pelletizer is measured and a signal is established responsive thereto representative of the temperature of the shell of the driver in the constant pellet temperature section required to achieve the desired drying rate. The actual shell temperature in the constant pellet temperature section is measured and compared with the predicted signal. A signal representative of the comparison is utilized to adjust the supply of heat to the dryer. The heat supply to the outlet end of the dryer can be separately controlled responsive to the temperature of the product leaving the dryer. Water can be injected into the inlet of the dryer in response to a sharp drop in water ow rate to the pelletzer.

This invention relates to method and apparatus for the controlled drying of agglomerates. In one aspect the invention relates to controlling the heat transfer rate in a carbon black pellet dryer responsive to the rate of addition of water to the pelletzer.

Carbon black as initially produced is a very fine, fluffy powder of exceedingly low density which readily flies into the atmosphere and presents numerous diiiculties in handling, shipping and storage, with which the industry is familiar. In order to increase its density, reduce flying and minimize handling difficulties, it is conventional to form small pellets of the carbon black which are relatively dustless, free-flowing, spheroidal pellets.

Such beads or pellets are usually produced by tumbling or otherwise agitating the carbon Iblack with a binding agent in a slowly rotating drum. The wet pellets from the rotating pelleting drum are then passed to a dryer wherein they are dried and the moisture content is reduced to less than 1 percent and usually about 0.1 percent. Conventional dryers such as heated rotating drums are used to remove the moisture from the well pellets. It is well known to those skilled in the art that the temperature of the dryer controls the ultimate quality of the dried pellets. If the temperature of the dryer is too hot, the dried pellets may be porous and have a spongy texture which offers little resistance to crumbling. ln extreme cases the drying drum may become so hot as to ignite the carbon black. On the other hand, if the dryer is too cold, the resulting pellets may be soft, crumble easily, and cake when stored. The temperature of the pellets as they are discharged from the dryer should be in the range of about 350 to 450 F. with a range of about 375 to 425 F. being preferred. Thus, any method to more effectively control the temperature of the dryer is a valuable contribution to the art.

One system which has been suggested manipulates the fuel flow rate to the burner in the dryer responsive to the temperature of the product leaving the dryer or in 3,482,327 Patented Dec. 9, 1969 ice the last portion of the dryer. However, the extensive dead time involved between a change in feed to the dryer and the appearance of this change at the effluent end of the dryer makes such a control system very diicult to maintain on an effective basis. Systems utilizing purge gas effluent temperature encounter dii-liculties since the amount of lire box gas and therefore the purge gas temperature varies with the amount of water vaporized, independent of dryer feed rate. Other systems involving the prediction of fuel rate required responsive to changes in water flow rate to the pelletizer, while generally satisfactory, are faced with the problems of thermal efficiency varying with load changes and a quadratic relationship between load and fuel required.

It has now been discovered that an effective control of the dryer can be maintained by predicting, responsive to the water llow rate to the pelletizer, the dryer shell temperature required t0 achieve a desired heat transfer rate to the pellets in the initial portion of the dryer. The predicted value is compared against the actual shell temperature to obtain a control signal to manipulate the heat input to the dryer. This can be accomplished by regulating the fuel flow rate to the burner in a direct lired dryer or the fuel flow rate to the furnace in a ue gas heated dryer. The heat input to the effluent end portion of the dryer can be controlled responsive to the temperature of the product leaving the dryer to serve as a trim control. Water can be injected into the dryer inlet if there is insufficient water in the pellet feed to prevent overheating.

Therefore, it is an object of the invention to provide improved method and apparatus for controlling the drying of agglomerated material. Another object of the invention is to control the rate of heat transfer to pellets in a dryer. Another object of the invention is to prevent overheating of carbon black pellets in a pellet dryer. Other objects, aspects and advantages of the invention will be apparent from a study of the specification, the drawing and the appended claims to the invention.

In the drawings FIGURE 1 is a schematic representation of a pelleting system in accordance with a presently preferred embodiment of the invention; FIGURE 2 is a schematic representation of a pelleting system in accordance with another embodiment of the invention; FIG- URE 3 is a graphical representation of the response of the system of FIGURE 1 to an increase and a subsequent decrease in carbon black feed rate to the dryer; and FIGURE 4 is a graphical representation of the response of a pelletizing system wherein the fuel ow rate is varied responsive to the temperature of the product leaving the drver.

Referring now to FIGURE 1, loose flocculent carbon black is fed into pellet mill, or mixer, 11 through conduit 12. A liquid binder, for example water, which can contain a very small amount of molasses, is passed by way of conduit 13 into mixer 11. The rate of flow of water through conduit 13 is manipulated by means, not shown, responsive to the rate of addition of carbon black to the mixer to maintain the ratio of binder to carbon black substantially constant at a desired value. One suitable system is to vary the ow rate of water responsive to the electrical power input required to operate the agitator of the mixer. Another system varies the flow rate of water to the pelletizer responsive to the output of a weigh conveyor in the carbon black transporting line. The resulting agglomerates or pellets are passed through a line 14 into a polisher 15 wherein the agglomeration action is continued. The wet pellets are passed from polsher 15 through line 16 into the inlet end of pellet dryer 17.

A suitable fuel, for example natural gas, fuel oil, or the off-gas from the carbon black lters, is passed by way of conduit 21 into a furnace 22. Air is passed by way of conduit 23 into and through preheater 24 in indirect heat exchange with the hot gases in furnace 22 and then through conduit 25 into furnace 22 wherein the air is admixed with the fuel to form hot combustion gases. The hot combustion gases contact preheater 24 and then pass through line 26 to and through branch conduits 27a through 27h into the jacket 28 surrounding the shell 29 of pellet dryer 17. Each of branch conduits 27a through 27h can be provided with a damper, 30a through 30h, respectively. The hot combustion gases pass around shell 29 and exit jacket 28 by way of conduits 31a, 31b and 31e which .are connected through conduit 32 to a vent or other point of utilization. A conduit 33 is connected between conduit 32 and the etlluent end of shell 29 to fpass a portion of the hot combustion gases through the interior of shell 29 in countercurrent ow relationship to the carbon black pellets. This portion of the combustion gas serves as a purge gas to carry steam out of the dryer by way of conduit 34. A blower 35 is provided in conduit 34 to withdraw the purge gas containing steam and to maintain the pressure in shell 29 slightly below atmospheric pressure to prevent leakage of carbon black from the system. The wet pellets passing through conduit 16 to dryer 17 are preferably preheated to a suitable temperature, for example on the order of 150 F. The preheated wet pellets enter dryer 17, which is rotated on its horizontal axis by means not shown. The pellets are rapidly heated upon entry into dryer 17 to the operating temperature, for example on the order of 200 F. The pellets achieve the operating temperature within approximately one foot of the inlet to the dryer and remain at the operating temperature for approximately two-thirds of the length of the dryer due to the plateau in the heat input versus temperature relationship resulting from the vaporization of the water. At a point approximately two-thirds of the way through the dryer, suicient moisture has been evaporated to permit an increase in the temperature of the pellets. The pellets are heated through the remainder of the dryer to further lower the water content and to achieve an euent temperature of the pellets leaving the dryer by way of conduit 36 in the range of about 375 F. to about 425 F.

A llow measuring sensor 41 is operatively connected to conduit 13 and produces a signal representative of the ow rate of water therethrough. For sake of simplicity, the ow sensor is illustrated as an orifice, it being recognized that suitable square rooting mechanism to achieve a linear flow signal can be included in the case of the orifice type flow sensor, or that other flow sensors such as turbine flow sensors can be utilized. Where the water flow rate contains high frequency oscillation, as in the oase where the water ow rate is regulated responsive to the electrical power input to mixer 11, the ow signal can be passed to a filter 42 to smooth out the ow signal. An example of a suitable filter 42 is the Taylor Instrument Company Model 588104 pneumatic pulsation damping unit. The filtered llow signal is applied to one input of ratio relay 43. As it is desirable to maintain a minimum temperature of the shell 29 of dryer 17 during start-up or temporary interruptions of the pelletizing operation, ratio relay 43 can be utilized to produce an output signal represented by the following relationship:

where SR is the output of ratio relay 43, SF is the linear flow signal from ow sensor 41, K1 is a proportionality constant, and K2 is a value equal to the minimum temperature of shell 29 at zero water llow to mixer 11. The minimum temperature for the shell 29 is generally the `4 operating temperature, that is, the constant temperature plateau for the wet pellets at which vaporization of the water occurs without significant heating of the pellets. The output signal SR is representative of the predicted temperature of that portion of shell 29 which is coextensive with the constant operating temperature region of the wet pellets which will be required to achieve the heat transfer rate necessary to vaporize the water at the rate it is flowing through conduit 13. This relationship follows from the equation:

wherein:

.q is time rate of heat transfer, B.t.u./hr.,

As the operating temperature lplateau TP and the other factors remain constant, it is readily seen `that the heat transfer rate varies directly with variations in the temperature of the external surface of shell 29 in the pellet temperature plateau region of the dryer. An example of a suitable ratio relay 43 is the Taylor Instrument Company Model NF1151 pneumatic ratio unit.

The output signal of ratio relay 43 is applied to the set point input of temperature recorder controller 46. A temperature sensor 47, for example a Honeywell Model RL-l radiation pyrometer, senses the external skin temperature of shell 29 at a position which is within the constant pellet temperature plateau region of the dryer. The electrical output of temperature sensor 47 is applied to the signal input of millivolt-topressure transducer 48. A bias value is applied to bias input 49 of transducer 48 and the output of transducer 48 is applied to the input of square root extractor 51 with the output of square root extractor 51 being applied to the measurement input of temperature recorder controller 46. While, in accordance with the Stefan-Boltzmann law, the detected energy is representative of the fourth power of the temperature, it has been found, for the operating range encountered in the carbon black pellet dryer, the square root of the difference between the output of the radiation pyrometer and the bias value 49 is sufliciently linear for the desired control purpose. However, if desired, two square root extractors could be utilized in series to obtain the fourth root of the output of the pyrometer. An example of a suitable transducer 48 is the Taylor Instrument Company Model 700TD1333 millivolt-to-pressure transducer. Square root extractor 51 can be a Taylor Instrument Company Model 359RF pneumatic square root extractor. The output of temperature controller 46 is representative of a comparison of the actual shell temperature represented by the output of square root extractor 51 and the predicted shell temperature represented by the output of relay 43. Controller 46 can be a two mode controller with proportional plus reset. The output of temperature controller 46 is applied to the setpoint input of flow recorder controller 52 which manipulates valve 53, operatively located in conduit 21, responsive to a comparison of the actual flow rate of the fuel in conduit 21, as indicated by tlow sensor 54, with the setpoint signal. The output of flow sensor 54 is applied to the measurement input of ratio controller 55. A signal representative of the desired ratio of air to fuel is applied to setpoint input 56 of controller 55. The output of controller 55 represents the required air flow rate and is applied to the setpoint input of the ow recorder controller 57, which manipulates the valve 58, located in conduit 23, responsive to a comparison of the setpoint signal with the actual flow rate as indicated by ow sensor 59. An example of a suitable controller 55 is a Taylor Instrument Company Model 105NF1151 pneumatic ratio unit. Where significant delay is encountered between a measurement by flow sensor 41 and the corresponding water reaching dryer 17, suitable first order or multiple order lags can be inserted in the control system to account for such delay.

Referring now to FIGURE 2, there is illustrated a modified version of the system of FIGURE 1. Flocculent carbon black is passed through conduits 112a and 112b to mixers 111a and 111b, respectively. Water is passed through conduits 113a and 113b to mixers 111a and 111b. The output of mixers 111a and 111b is passed to polisher 115 with the output of the latter being passed through line 116 to pellet dryer 117. A suitable fuel is passed through conduits 120 and 121 into and through branch conduits 127a through 127f to burners 161a through 161f, respectively, located inside of the lower portion of jacket 128 which surrounds shell 129. Air is admitted into jacket 128 by way of opening 123. The combustion gases are withdrawn from jacket 128 by way of conduits 131a through 131d and passed into conduit 132. A portion of the hot combustion gases are withdrawn from conduit 132 and passed by Way of conduit 133 into the effluent end of shell 129 for countercurrent flow to the carbon black pellets in shell 129 as purge gas. Conduit 134 connects the inlet end of shell 129 to blower 135 for the Withdrawal of the purge gas and steam from the shell 129.

A rst signal representative of the flow rate of Water through conduit 113a is transmitted by flow sensor 141a to adder 162. A second signal representative of the How rate of water through conduit 113b is transmitted by flow sensor 141b to a second input of adder 162. As in the case of the system of FIGURE 1, filtering means can `be utilized to smooth out the water flow rate signals if desired. The output of adder 162 represents the total water flow rate to the mixers and is applied to one input of adder 163, through delay 164 to a rst input of subtractor 165, and directly to a second input of Subtractor 165. The output of Subtractor 165 represents the difference between the instantaneous water flow rate and a delayed function of a previously existing water ow rate, and thus is indicative of any significant changes in the water flow rate to the mixers. Subtractor 165 is biased to produce an output signal only when the instantaneous ow rate signal is less than the delayed flow rate signal or, in other words, when a decrease in the total Water flow rate to the mixers has occurred. The output signal of subtractor 165 returns to zero -When the delayed flow rate signal drops to the value of the instantaneous flow rate signal. The output of Subtractor 165 is applied to the set point input of flow recorder controller 166 which manipulates valve 167 positioned in conduit 168 responsive to a comparison of the set point and the actual flow rate through conduit 168 as indicated by flow sensor 169. Thus, upon the occurrence of a positive output of Subtractor 165, flow controller 166 opens valve 167 to` pass water through conduit 168 into the inlet end of shell 129. This prevents overheating of the carbon black pellets during the time require-d for the Iburner heating system to respond to the control system. The output of Subtractor 165 is also applied to a second input of adder 163 to produce a signal representative of the total ow rate of water being introduced into dryer 129 by way of conduits 113a, 113b and 168. The output of adder 163 is applied to an input of ratio relay 143 to produce an output signal representative of the temperature of the outer surface of a portion of the section of the shell 129 which is coextensive with the constant pellet temperature plateau operating region which is required to vaporize the water from the pellets at the rate it is being introduced by way of conduits 113a, 11311 and 168. Ratio relay 143 has the same relationship between its signal input and output as ratio relay 43. A tem-perature sensor 147 senses the radiation from the external surface of shell 129 and transmits a signal representative thereof to transducer 148. Bias value is applied to bias input 149 and the output of transducer 148 is applied to the input of square root extractor 151. The output of square root extractor 151 is representative of the temperature of the external surface of shell 129 in the constant pellet temperature plateau region and is applied to the measurement input of temperature controller 146. The output of temperature controller 146 manipulates valve 171 located in conduit 121 to thereby vary the rate of flow of fuel to burners 127a through 1271 to maintain the actual shell temperature at the predicted value.

Conduit 172 supplies fuel from conduit 120 to burners 161g and 161k located in jacket 128 under the eluent end of shell 129. Valve 173, located in conduit 172, can be manipulated by temperature recorder controller 174 responsive to a comparison of the desired product temperature represented by set point 175 and the actual temperature of the dried pellets passing through conduit 136 as indicated by temperature sensor 176. Thus, valve 171 manipulates the rate of flow of fuel to burners 161:1 through 1611 to thereby vary the shell temperature in the constant pellet temperature plateau region while valve 173 varies the rate of flow of fuel to burners 161g and 161k to vary the shell temperature in the effluent end of the shell downstream of the constant pellet temperature plateau region. In this manner, control of valve 171 regulates the rate of transfer of heat to the wet pellets while water is being evaporated at a substantially constant temperature, and valve 173 regulates the transfer of heat to the pellets which have passed out of the constant pellet temperature plateau region to control the final temperature of the pellets as they leave the dryer.

Referring now to FIGURE 3, curve 201 lis a graphical representation of the flocculent carbon black feed rate through conduit 12 to mixer 11 in the system illustrated in FIGURE 1. Curve 202 represents the temperature of the hot combustion gases passing through conduit 26 while curve 203 represents the ow rate of the hot combustion gases through conduit 26. Curve 204 represents the rate of removal of water by way of the steam and purge gas mixture passing through conduit 34. Curve `205 represents the temperature of the gases passing through conduit 34. Curve 206 represents the location in the last twenty feet of the dryer, which is sixty feet long, at which the temperature of the pellets begins to rise above the constant operating temperature plateau. lCurve 207 represents the temperature of the pellets as they leave the dryer and enter conduit 36. Curve 201 contains a step increase 211 in the carbon black feed rate and a step decrease 212 in the carbon black feed rate. Curves 202 through 207 show the response of the respective factors of the system to these step changes under the control system illustrated in FIGURE l.

Referring now to FIGURE 4 there are illustrated graphical representations of the various factors in the drying system of FIGURE 1 utilized to obtain the curves of FIGURE 3 except that the control elements 41, 42, 43, 46, 47, 48 and 51 were omitted and the set point of flow controller 52 was adjusted by the output of a temperature controller responsive to the temperature of the pellets passing through conduit 36. Curve 301 represents the occulent carbon black feed rate and contains a step increase 311 and a step decrease 312. Curve 302 represents the temperature of the combustion gases passing through conduit 26 while curve 303 represents the llow rate of these combustion gases. Curve 304 represents the rate of removal of water through conduit 34 while curve 305 represents the temperature of the gases passing through conduit 34. Curve 306 represents the position in the last portion of the reactor at which the carbon black becomes substantially dry and the temperature thereof begins to increase. Curve 307 represents the temperature of the pellets passing through conduit 36.

An examination of the effects on the various factors due to the step increase and step decrease in carbon black flow rate for the control system represented by FIG- URE 3 and the control system represented by FIGURE 4 readily indicates the superiority of the control system represented by FIGURE 3 over that of the control system represented by FIGURE 4. This is particularly apparent in..the effect on the product temperature of the pellets leaving the dryer and the location in the dryer at which the temperature of the pellets begins to increase above the constant operating temperature plateau.

Reasonable variations and modifications are possible within the scope of the foregoing disclosure and the drawings of the invention.

I claim:

1. I n an apparatus for agglomerating finely divided solids, which comprises a mixer; means for introducing said finely divided solids into said mixer; conduit means for introducing a liquid binder into said m'urer; a dryer having an elongated shell; means for passing wet agglomerates from said mixer into the inlet end of said elongated Shell; means for withdrawing dried agglomerates from the outlet end of said elongated shell; and heating means for heating the exterior surface of said elongated shell; the improved control system comprising means for producing a first signal representative of the flow rate of said liquid binder through said conduit means to said mixer; means responsive to said first signal to establish i a second signal representative of the temperature of the external surface of said shell in the region of said shell wherein the temperature of the wet agglomerates remains substantially constant while a portion of the liquid binder contained in the wet agglomerates is being vaporized, required to vaporize the binder in said region at the rate binder is added to said finely divided solids; means for establishing a third signal representative of the actual temperature of the exterior surface of said shell in said region; means responsive to said second and third signals for controlling said heating means to vary the heat supplied to said shell in said region responsive to the difference between said second and third signals.

.2. Apparatus in accordance with claim 1 wherein said mlxer is a pellet mill, said dryer further comprises a jacket surrounding said elongated shell, said heating means comprises means for passing hot fluid through said jacket in contact with the external surface of said shell, and said means for controlling said heating means comprises means for controlling the rate of fiow of fuel to said heating means responsive to the difference between said second and third signals.

3. Apparatus in accordance with claim 1 wherein said means to establish a second signal comprises a ratio relay having an input and an output, means for connecting the output of said means for producing a first signal to said lnput of said ratio relay, the output signal from said ratio relay being said second signal and representable as:

SR=K1SFK2 wherein:

SR is said second signal, K1 is a proportionality factor,

` K2 is the desired temperature of said shell at zero flow rate of binder through said conduit means, and SF is said first signal representative of the flow rate of binder through said conduit means.

4. Apparatus in accordance with claim 3 wherein said means for establishing a third signal comprises a radiation pyrometer positioned to detect the radiation from the external surface of said shell in said region; a voltage to pressure transducer having a signal input, a bias input and a pressure output; means connecting the output of said radiation pyrometer to said signal input of said transducer; means for applying a bias signal to said bias input of said transducer; a square extractor with the input thereof connected to said pressure output of said transducer.

5. Apparatus in accordance with claim 4 wherein said means for controlling said heating means comprises a temperature controller having a measurement input, a setpoint and an output; means for applying said second signal to said setpoint; means for connecting the output of said square root extractor to said measurement input; and means responsive to said output of said temperature controller to control said heating means.

6. Apparatus in accordance with claim 5 wherein said heating means comprises a furnace, second conduit means for passing fuel to said furnace, third conduit means for passing air to said furnace, a jacket surrounding said shell, fourth conduit means lfor passing hot combustion gases from said furnace through said jacket in heat exchange relationship with the, exterior surface of said shell, and wherein said means to control said heating means comprises means responsive to the output of said temperature controller for varyingthe ow rate of fuel through said second conduit means, and means responsive to the ow rate of fuel through said second conduit means to vary the rate of flow of air lthrough said third conduit means to maintain a desired ratio of air to fuel going into said furnace.

7. Apparatus in accordance with claim 1 wherein said mixer comprises `a plurality of pellet mills, said means for introducing finely divided solids comprises means for introducing finely divided solids into each of said plurality of pellet mills, said conduit means comprises a plurality of conduits` each connected to a respective one of said pellet mills, saidmeans for passing Wet agglomerates connects the output of each of said pellet mills to the inlet end of said elongated shell, and said means for producing a first signal comprises a plurality of flow sensors each being connected to a respective one of said plurality of conduits, an adder having a plurality of inputs, and means connecting the output of each of said flow sensors to a respective one of said plurality of inputs of said adder.

8. Apparatus in accordance with claim 1 wherein said means for producing a` first signal comprises means for sensing the flow rate of liquid binder through said conduit means and establishing a fourth signal representative thereof, delay means, a subtractor, an adder, means for applying said fourth signal to the input of said delay means, to an input of said subtractor and to an input of said adder, means connecting the output of said delay applying the output of said subtractor to a second input of means to a second input of said subtractor, means for said adder, the output of said adder being said first signal, and means for injecting liquid binder into the inlet end of said elongated shell responsive to the output of said subtractor.

9. Apparatus in accordance with claim 1 wherein said heating means comprises first heating means for heating said shell in said region and a second heating means for heating said shell downstream of said region, said means responsive to said second and third signals for controlling said heating means comprises means for regulating said first heating means responsive to the difference between said second and third signals, and further comprising means for regulating said second heating means responsive to the temperature of the agglomerates being withdrawn from said outlet end of said elongated shell.

10. In a method of pelleting carbon black which comprises passing finely divided carbon black to a pelletizing zone, passing a liquid binder into said pelletizing zone and therein admixing said finely divided carbon black and said liquid binder to form pellets, passing the thus formed pellets into the inlet end of an elongated drum dryer, passing a heating fiuid into heat exchanging relationship with the exterior surface of said elongated drum dryer, and withdrawing dried pellets from the outlet end of said elongated drum dryer; the improved control procedure comprising measuring the rate of ow of said liquid binder into said pelletizing zone and establishing a rst signal representative thereof, establishing responsive to said 'rst signal a second signal representative of the temperature of the external surface of said drum dryer in the region of said drum dryer wherein the temperature of the wet pellets remains substantially constant while a portion of the liquid binder contained in the wet pellets is being vaporized, required to vaporize the binder in said region at the rate binder is being passed to said pelletizing zone, establishing a third signal representative of the actual temperature of the exterior surface of said drum dryer in said region, and varying the degree of heating of said References Cited UNITED STATES PATENTS 8/1959 Heller 34-12 3/ 1965 McGregor et al. 263-34 JOHN J. CAMBY, Primary Examiner U.S. C1. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 31482 327 Dated December 9, 1969 Inventor(s) Dennis L. Butcher It; is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as show-n below:

Column 8 delete line 49; Column 8 after line 50 insert applying the output of said subtractor to a second input of -f.

' SIGNED AND SEALED APR 281970 5m) Attest:

Edward M member Ir" WILLIAM E. som, JR. Attestng Officer Commiszeionecr` of Patents

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