US 3238634 A
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3 Sheets-Sheet 1 R. R. GOINS March 8, 1966 PROCESS AND APPARATUS FOR DRYING WET PARTICULATE SOLIDS Filed April 9, 1962 om: m2
March 8, 1966 R. R. GOINS PROCESS AND APPARATUS FOR DRYING WET PARTICULATE SOLIDS 3 Sheets-Sheet 2 ATTORNEYS R. R. GOINS March 8, 1966 PROCESS AND APPARATUS FOR DRYING WET PARTICULATE SOLIDS Filed April 9, 1962 3 Sheets-Sheet 5 TO FILTER SET POINT DRY l PELLETS SECOND DRYER FIRST DRYER WET PELLETS |88 AIR l J,
FURNACE PELLETS INVENTOR. R. R. GOINS FUEL- J FEED- ATTORNEYS pellets which must be dried before packaging.
United States Patent 3,238,634 PROCESS AND APPARATUS FOR DRYING WET PARTCULATE SOLIDS Robert R. Goins, Bartlesville, kla., assigner to Phillips Petroleum Company, a corporation of Delaware Filed Apr..9,.1962, Ser. No. 186,038 19 Claims. (Cl. 34-10) This invention relates to a process and apparatus for drying wet particulate solids. A specific aspect of the invention pertains to a process and apparatus for drying Wet pelleted carbon black.
Various powdered materials are wet pelleted into small Carbon black, catalysts, adsorbents, fertilizers, etc., are some of the materials which must be dried in particulate form before storing or packaging. ln drying these solids, rotary drum type dryers are conventionally utilized. The drum is rotated around its horizontal axis while feed is introduced to one end and dried solids are delivered from the other end. This type dryer is heated by means of hot combustion gas formed in a furnace under or afyjacent the dryer. One of the problems encountered is the control of the shell temperature of the dryer so that the drying is done efficiently without overheating and/ or igniting the material being dried. When utilizing a drum dryer in drying carbon black pellets, it has been found particularly difficult to control the heat input to the dryer so as to properly dry the pellets of carbo-n black without overheating of the black and the dryer.
It has been proposed to dry pellets in a fluidized bed dryer. This drying technique has been more or less successful but due to the vast heat requirements to vaporize the water from the wet pellets, the dryer must be of large volume capacity in order to allow suflicient heat input. The large capacity dryer requirement means a long residence time of the solidsA in the dryer which in turn increase the attrition of the solids and the proportion of the solids which pass out with the effluent gasv as fines and must be repelleted and recycled to the dryer. This, of course, decreases the efficiency and -increases the cost of the drying process.
Accordingly, it is an object of the invention to provide an improved process and apparatus for drying particulate solids. Another object of the invention is to provide a process and an apparatus for drying particulate solids which are highly ecient and effects a minimum of attrition and production of fines in the solids. A-further object is to provide a process and arrangement of apparatus for controlling the drying of particulate solids. It is also an object of the invention to provide a process and apparatus for drying particulate solids, such as wet carbon black pellets, which operates more economically than heretofore. Other objects will become apparent to one skilled in the art upon consideration of the accompanying disclosure.
A broad'aspect of the invention comprises utilizing hot off-gas from a carbon black or other type reactor as the drying gas for fluidizing and drying wet particulate solids, particularly, carbon black pellets. The solids to be dried are either introduced directly into the off-gas line and transported into a fluidized bed drying zone in the line, or off-gas is taken directly from the off-gas line 3,238,634 Patented Mar. 8, 1966 ice In the application of the process in which smoke is taken from the reactor off-gas line or smoke header, it is advantageous to utilize fluidized bed dryers arranged in series and to effect most of the drying in the iirst bed and residual drying in the second bed. In this manner the major portion of the water all but about2-50 weight percent) is driven from the pellets or other solids at a relatively low bed temperatureV withhigher fbed temperature being utilized in the second dryer. Also, the second dryer is made considerably smaller than the first dryer so as to reduce the residence time of the solids therein and reduce the attrition and proportion of solids converted to fines. The operation of two dryers in series is not limited to the use of smoke or off-gas as the drying gas but, on the contrary, advantages accrue to this technique when utilizing steam, air, CO2, and other conventional drying gases.
When drying wet carbon black pellets containing about 43-57 Weight percent water (conventional Water content of wet pelleted carbon black) fines resulting from abrasion of the pellets run as high as l0 percent or more by ,Weight of the pellets fed to the dryer. These fines must be returned to the pelletizer and recycled thru the dryer as wet pellets which proportionately increases the heat load on the dryer. It has been found that Wet carbon black pellets can be dried in two separate beds connected in series With increased eflciency and less fines loss. To illustrate the advantage of utilizing two uidized beds for drying carbon black pellets having a moisture content of about 50 weight percent, the following example is presented.
EXAMPLE Runs were lmade utilizing a 12" diameter iluidized bed dryer with different air inlet temperatures. Fines in the dryer efuent gas were collected in a cyclone separator. The data obtained are presented in the table below.
In a similar run utilizing an air inlet temperature of 1400 F., the -cyclone product (fines) amounted to a little more than l() percent of the feed `on a dry basis.
. It should be noted that operating with a lower drying gas temperature and drying to a lower moisture content such as 3.5 weight percent as in Run No. 1 produces only `2.7 percent fines as compared to 6.5% lines when drying to a moisture content of 0.6 weight percent as illustrated in Run 2. By oper-ating with two beds, the first one under conditions of Run No. 1, and then passing the semi-dry bla-ck into the second bed operating near conditions of Run 2 it is possible .to substantially reduce the lines formed in the process. The second bed is operated at a minimum residence time by reducing the relative size of the dryer. `Improvements obtained in this 2-bed operation include (1) efficiency is increased because most of the drying is done at a lower temperature, (2) abrasion of the pellets is minimized, (3) contact time in the second vessel can :be controlled (as well as the temperature) to control the amount of after treating without affecting the efficiency of the drying operation .in the primary dryer, and (4) special atmosphere or treating gas can be utilized in the second drye-r for after-treating the black while reducing the moisture content to less than about 1 percent by weight.
Another aspect of the invention comprises drying the wet solids in a first fiuidized bed, `after-treating the dried solids in a second fluidized bed, and cooling the hot solids from the second bed in a third `fiuidized bed. In this ytechnique cooling gas pased thru the cooling zone as a fluidizing gas is preheated and passed to the treating zone in admixture with other hot gas to provide the optimum temperature for the after-.treating step. The hot treating gas is then passed into the drying zone as fiuidizing and drying gas. In this process, a great economy of heat is obtained.
Another aspect of the invention comprises controlling the heating conditions in a pair of dryers operated in series by sensing the temperature yof the effluent gas from the second dryer and controlling the heat input to the second dryer and simultaneously sensing the variations in the heat input to the second dryer and utilizing the sensed variable to control the heat input to the first dryer. This may be accomplished by different apparatus arrangements as more fully set forth below.
A more complete understanding of the invention may be obtained by consideration of the accompanying schematic drawing of which FIGURE l shows an arrangement yof apparatus in accordance with one aspect of the invention; FIGURE 2 shows an arrangement of apparatus in accordance with another aspect of the invention; FIG- URE 3 shows one arrangement of apparatus and controls for effecting one laspect of the invention; FIGURE 4 shows another arrangement of controls and apparatus for effecting another aspect of the invention; and FIGURE 5 shows apparatus in accordance with Va further embodiment of the invention.
Referring to FIGURE 1 a pair of carbon black reactors connect with a common smoke header 12 which feeds into smoke line 14 leading to cyclone separator 16. Water line 18 connects with line 14 to supply quench water to the smoke. Line 20 connects cyclone 16 with bag filter 22 which .feeds black into line 24 containing pulverizer 26. Off-gas from the bag filter is taken off through line 28, a portion venting to the atmosphere and another portion being recycled through line 30 to line 32 leading into blower 34. Carbon black recovered from cyclone 16 and from bag filter 22 is delivered through lines 24 `and 36 to pneumatic conveyor 38 for transport to surge vessel 40. Carbon black from surge vessel 40 passes through line 42 into wet pelletizers 44 which are supplied rwith water, which may contain additives such as molasses, from a line 46. A-ll of .the apparatus thus far described is conventional in modern carbon black pelleting plants.
Wet pellets containing from about 43 to about 57 percent moisture by weight pass through line 48 into transport drying line 50 leading into the bottom of fluidized bed dryer 52. Hot smoke for the transport drying line 50 is dra-wn `from smoke line 14 by means of lines 51 and 54. Other gas may be introduced through line 56 as tempering .gas to control the temperature and/ or to change the character of the drying gas. Air, steam, CO2, etc., maybe introduced at this point.
The term smoke, `as used in the carbon black art and herein, denotes the hot efiluent from a carbon black reactor comprising a suspension of finely divided carbon black in combustion gases.
Efliuent gas from dryer 52 is passed via line 60 to line 20 or to ,bag filter 22. Dried pellets from dryer 52 are taken off by means of conduit 62 which leads into the lower section of dryer 64. Fluidizing and drying gas for dryer 64 may also be smoke or off-gas obtained from line 54 through lines 66 and 68. Here again, additional drying gas of 4a different character may be introduced through line 70.
Effluent gas from dryer 64 is passed via line 72 to finesseparating cyclone 74 or it may be passed via line 76 to line 20 for passage to bag filter 22 to separate fines therefrom. In the event the fines are recovered in cyclone 74, they are passed through line 78 to pneumatic conveyor 38 for recycle to the pelletizers.
In the event only one fluidized bed dryer is utilized to accomplish the drying step, dried pellets in line 62 are passed via line 80 directly to bagging or storage. When both dryers are utilized, eiuent dry pellets are passed via line 82 to line 80 for passage to bagging or storage.
The degree of completion of the drying process in dryer 52, when dryer 64 is not used, is controlled by manipulation of the flow rate of drying gas to the process by operation of valves 84 land 86 land 'by sensing the temperature of the efluent drying gas in line 60 and feeding this signal from transmitter 88 to temperature recorder controller 90 which positions motor valve 92 in water line 94, thereby manipulating the amount of quench water ladded to the efiluent smoke and, indirectly, the offgas temperature in line 60 from dryer 52.
Referring to FIGURE 2, a fiuidized dryer is provided with a wet pellet inlet line 102, inlet drying gas line 104, and an efiiuent gas line 106. Dried pellets are taken off through line 108 and passed to the lower section of uidized treater 110. Fuidizing gas from treater 110 is supplied through line 112 and eiuent gas is passed through line 114 to line 104 as drying gas to dryer 100. Combustion gas is added through line 116 as needed to supplement the drying gas from line 114 in sufiicient volume to provide a fluidizing flow rate and at sufficient temperature to provide the desired drying gas temperature in dryer 100. Effluent treated pellets from treater 110 are passed through line 118 to cooler 120 for cooling to a temperature satisfactory for bagging or storing of the pellets.
Air or other gas for cooling the treated pellets is introduced to cooler 120 through line 122. Off-gas from dryer 100 may be passed through line 124 into line 122 to supplement the cooling gas when desired. This off-gas may also be recycled to eiuent line 126 from cooler 120 through line 128. All or any part of the gas in line 126 may be passed to line 112 as treating gas through line 30. A substantial portion of the treating gas in line 112 is supplied from line 132, preferably as combustion gas or superheated steam. Cooled pellets are withdrawn from cooler 120 through line 134.
Fluidizing vessels and the depth of the uid beds therein are sized to give proper hold up time and to provide as well as to require compatible volumes of gas as needed in the different steps. Integrated gas temperature and volume controls are used to maintain proper conditions in the beds. Volume controls are needed to produce the necessary fiuidization velocities in the beds. Temperatures within the beds are principally controlled by manipulation of the inlet temperatures of the gases to each of the beds. Desired compositions of the gases used in the drying and treating beds can be achieved by recycle of off-gas from the dryer to the cooling bed. To further reduce oxygen (if desired) the air used in the cooling bed can be used as combustion air for the treater and dryer. Cyclones may be required on the gas efiiuent from each of the beds to remove small amounts of fines.
Drying in the arrangements shown in FIGURES l and 2 can be accomplished in the first fiuidized bed at bed temperatures in the range of about 275 to 300 F. with short residence time; and drying to around 3.5 percent moisture can be effected at about 175 F. as shown in the illustrative example above. Drying is done in the first fluidized bed preferably in the temperature range of to 300 F. Pellets are then passed to the second drying and/or treating bed Where temperature is raised to the range of about 500 to 1200" F. to complete the drying and to control the properties of the black. Carbon black pellets then pass to the cooling bed (FIG. 2) for cooling to the range of about 200 to 500 F. and, preferably, below 400 F. for bagging or storage.
Referring to FIGURE 3, a rotary dryer. 140 is provided with a wet pellet inlet line 142 and a dried pellet eluent line 144. Burners or burner means 146 below the dryer drum are supplied air land fuel gas from line 148. These burners or burner means may be radiant burners located either outside or inside of the dryer shell. Off-gas is vented through stack 150 or any portion thereof may be passed via line 151 to line 160 to supplement the drying gas in line 160. A second dryer in the form of a lluidized bed dryer 152 is connected with line 144 to receive partially dried pellets. Hot drying and luidizing gas is supplied by burning an air-fuel mixture in furnace 154, supplied through fuel line 156 and air line 158. The hot combustion gas is introduced to the bottom of dryer 152 via line 160. OIT-gas from dryer 152 passes through line 162 to the filter of the carbon black plant.
' In the operation of the dryers of FIGURE 3, the temperature of the effluent gas in line 162 is sensed and a signal is emitted by transmitter 164 to temperature-recorder-controller 166 which manipulates motor valve 168 in response to the signal received so as to add more fuel upon sensing a lower temperature and cut down on the rate of fuel flow when a higher temperature is sensed than a predetermined operating temperature. In this arrangement the flow of air in line 58 is maintained substantially constant by means of motor valve 170, controller 171, and flow transmitter 172. In order to proportion the'drying load between the two dryers (140'and 152), the flow rate of fuel in line 148 is also manipulated by means of temperature-recorder-controller 174 which is in control of motor valve 176 and receives a measurement signal from transmitter 178 in response to the sensed temperature of the gas in line 160. In order to protect the equipment, temperature transmitter 175 senses the shell temperature of the rotary dryer and acts through Acontroller 174 to limit fuel gas flow through line 148 via valve A176 to prevent exceeding the maximum set temperature for the safe operation of the dryer.
To illustrate the operation of the control system of FIGURE 3, when the drying load on the system (dryer 140 and dryer 152) changes (for example, increases) by an increase inthe feed rate of wet pellets or by an increase in the initial water content of the pellets, this effect passes to dryer 152 by virtue of a higher Water content of the pellets in line 144 which subsequently causes the temperature of the off-gas in line 162 to decrease, since more water enters the dryer via the pellets but the rate of heat input via line 160 has not yet been increased.
This change in temperature in line 162 is sensed and the control system changes the heat input to both dryers. In response to this off-gas (line 162) temperature decrease, rcontroller 166 increases the opening of valve 168,.thus increasing the fuel gas ow rate, which raises the combusted gas temperature and thereby increases the heat input to dryer 152 via line 160. This increased heat input dries the pellets discharged by line 153 to a greatercreased drying loadfrom the iluid bed dryer to the rotary dryer. This system is doubly advantageous in that (l) it brings about load sharing of two serially operated units performing the same general function and (2) the rapid changes in drying load are compensated for in the unitv which can be manipulated more rapidly, and the sloweroccurring drying load changes, which persist for some period of time, are rst corrected by the fluid bed dryer, with the increased load being transferred (gradually during a period of time) to the greater drying capacity unit (rotary dryer) thus leaving the faster-correcting fluid bed unit in the middle of its drying capacity range. ready to -compensate for the next drying load transient condition.
When the heat load on dryer decreases because of lower feed rate of wet pellets or lower water content, the opposite adjustment is made in valves 168 vand 176 by the control system. In the arrangement shown in FIGURE 3, dryer 140 may also be a lluidized bed dryer (as illustrated in FIGURE 4) with a different set of controls.
Referring to FIGURE 4, a rst dryer 180, which may be either a rotary or a fluidized bed dryer, is `supplied wet pellets thru line 182 and heat for drying thru line 184 from furnace 186, Air at a constant rate is fed to furnace 186 fvia line 188 and fuel gas via line 190 under the control of motor valve 192. Etlluent drying gas is vented thru line 194 or passed to the filter, and eluent semi-dry pellets are passed via line 196 to second fluidized bed dryer y198. Fluidizing and heating gas is passed into the bottom of dryer 198 thru line 200 whichrconnects with furnace 202. This furnace is supplied an air-fuel mixture thru line 204 under the control of motor valve 206. Effluent dry pellets are recovered thru line 208 and eluent drying gas from the second dryer passes to the lter via line 2.10.,
The control system for operation of the dryer of FIG- URE 4 comprises a temperature transmitter 212 responsive to the temperature in line 210 and emitting a signal proportional to the sensed temperature to TRC 214. Instrument 214 controls valve 206 Vin response to the sensed `temperature so as to increase the ow rate of combustible mixture to furnace 202 when the sensed temperature is below the desired (set point) temperature of the gas in line 210 or to decrease `the Illow rate to furnace 202 when the sensed temperature is above normal operating temperature. The heat input to dryer 180 is simultaneously controlled by an arrangement of instruments cornr prising ilow transmitter 216 and flow recorder controller 218 which is in control of motor valver192 so that upon an increase in flow rate in line 204, the flow rate of fuel in line 190 is also increased to proportion the heat loads on the two dryers. The opposite adjustment is made when the temperature in line 210 is too high, indicating abovenormal heat input to the dryers for the drying load imposed thereon.
To prevent the first dryers temperature from becoming excessive, as heretofore mentioned, each pair of transmitters -178 and 216 and 217 in FIGURES 3 and 4" may operate thru a low pressure selective relay included within TRC .174 and FRC 218, to select the lower signal (temp.) and pass it to its respective controller. Taylor Instrument Co., model SK 11359 is an illustration of this type of instrument.
An alternative control system on the .rst dryer of FIG- URE 4 is illustrated by line 220 which connects TRC 214 directly with ymotor valves =192 and 206 (eliminating transmitter 216 and controller 218) so that the signal from TRC 214 simultaneously either increases or decreases the flow thru the lines which these val-ves control to change the heat requirements of the process and simultaneously proportion the loads on the two dryers.
FIGURE 5 shows a fluidized bed dryer 230 positioned directly in smoke line 232 directly downstream of one or more carbon black reactors 234. Wet pellets are fed intothe lower section of dryer 230 thru line 236 and dry pellets are withdrawn thru line 238 from the top of the uidized bed 240. It is also feasiblel to introduce the pellets thru line 242 directly into smoke line 232 sufliciently upstream of dryer 230 to provide substantial transport drying of the pellets prior to their introduction to dryer 230.
Temperature control of the smoke to dryer 230 is effected by sensing the eflluent gas temperature by conventional means and transmittingV the sensed temperature by means of transmitter 244 to controller 2415 which operates motor valve 246 in water quench line 248. In this manner the eihuent temperature from the dryer is regulated by regulating the amount of quench Water introduced to the smoke stream.
When utilizing smoke from a carbon black reactor as drying and uidizing gas, the temperature of the smoke is usually controlled (by Water quench) in the range of 500 to 1500 F. and preferably 800 to 1500 F., but temperatures up to reactor outlet temperature -may be used. The gases from the dryer which contain fines from the pellets, as well as most of the original loose black from the smoke, pass thru the smoke line to the plant lters and thus eliminate the need for a separate filter for the dryer off-gas.
Advantages of the use of smoke as the drying gas include (1) elimination of need for fuel gas and equipment for burning same to produce hot gas, (2) smoke is completely inert (no free O2), (3) no extra lter and no extra load on regular filters of the plant, and (4) the dryer acts as an elutriator to remove fines so that product has less dust than product from a rotary dryer.
It is feasible to utilize smoke line 232 as a transport dryer to effect substantially the entire drying process and utilize vessel 230 as a cyclone separator to remove the dried pellets. In fact, drying of any wet particulate solids may be effected wholly by transport drying followed by separation of the dried particles from the hot transport gas in a cyclone separator, bag filter, or other suitable separation means.
In the drying of particulate coal (being transported in a slurry) before feeding same to a furnace, stack gas from the furnace can be utilized effectively as the drying gas in accordance with this invention. Transport drying is effective in this application.
Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.
1. A process for drying wet pellets of carbon black which comprises maintaining said pellets in a relatively deep and narrow fluidized bed in a hot fluidizing and drying gas in a drying zone so as to dry same to a moisture content below about 1 weight percent; passing the resulting dried pellets from an upper section of said bed to a treating zone and treating same with a hot treating gas therein; passing resulting treated pellets from an upper section of said treating zone to a cooling zone and contacting same therein with a cooling gas to cool same to a temperature below about 400 F.
2. A process for drying wet pellets formed from powdered carbon black and containing at least 40 weight percent water which comprises the steps of:
(1) passing said pellets into a first drying zone and drying same therein to a water content in the range of about 3 to about 25 weight percent;
(2) passing the partially dried pellets from step (1) into a second drying zone and maintaining said pellets therein in a relatively deep and narrow uidized bed by passing a hot drying gas upwardly therethru at a uidizing velocity;
(3) drying said pellets Iin the liuidized bed of step (2) to a moisture content below about 1 weight percent and causing the dried pellets to rise to the top of said bed; and
(4) withdrawing the dried pellets of step (3) from an upper section of said deep bed.
3. Apparatus for drying wet pelleted material which comprises in combination:
( 1) an upright vertically elongated cylindrical dryer providing a substantially unobstructed drying chamber having a wet pellet inlet, a bottom inlet for drying gas, a drying gas outlet in its top, a dried pellet outlet leading from an upper section thereof, and gas distributing means forming the bottom of said chamber;
(2) an upright cylindrical fluidized bed treater having a pellet inlet connected with the dried pellet outlet of 1) by conduit means, a treating gas inlet and distributing means in its bottom, a treating gas outlet in its top, and a treated pellet outlet in its upper section;
(3) conduit means connecting the drying gas inlet of (1) with the treating gas outlet of (2);
(4) an upright cylindrical liuidized bed cooler having a treated pellet inlet connected by conduit means with the treated pellet outlet of (2), a cooling gas inlet and distributing means in its bottom section connected with a cooling gas supply line, a cooling gas outlet in its top, and a cooled pellet outlet in an upper section thereof;
(5) conduit means connecting the cooling gas outlet of (4) with the treating gas inlet of (2); and
(6) a hot treating gas supply line connecting with the treating gas inlet of (2).
4. A process for drying wet carbon black pellets compacted from powdered carbon black and aqueous liquid which comprises the steps of:
(l) maintaining said pellets in a relatively deep and narrow uidized bed in a cylindrical -drying charnber by passing a hot drying gas upwardly therethru at a fiuidizing velocity;
(2) drying said pellets in the bed of step (1) to a moisture content below about 1 weight percent and casing the hot dried pellets to rise to the top of said bed;
(3) withdrawing the hot dried pellets of step (2) from an upper section of said bed and passing same to a cooling zone; and
(4) cooling the pellets in the cooling zone of step (3) to a relatively low temperature by contacting same with a cooling gas.
5. The process of claim 4 wherein the dried pellets from step (2) are passed into a iiuidized bed treating zone prior to passing same to steps (3) and (4) and are contacted therein with a hot uidizing and treating gas to materially treat same.
6. The process of claim 4 wherein said pellets are cooled in step (4) from a temperature substantially above to below 400 F.
7. The process of claim 2 wherein the wet pellets are dried in step (l) by entraining same in a hot drying gas to form a suspension thereof in said gas and passing the resulting suspension thru a transport drying zone to step (2).
8. The process of claim 7 wherein the drying gas of step 1) comprises essentially steam.
9. The process of claim 7 wherein the drying gas of step (l) comprises essentially air.
10. The process of claim 7 wherein the drying gas of step (1) comprises essentially combustion gas.
11. The process of claim 7 where in the drying gas of step (l) is hot smoke from a carbon black reactor.
12. The process of claim 11 including the steps of passing the smoke withdrawn from the dryer to a filter to recover carbon black therefrom and passing the recovered carbon black to a wet pelleting step to form said wet pellets.
13. The process of claim 2 wherein first said drying zone is a rotary drying zone.
14. The process of claim 2 wherein iirst said drying zone is a fluidized bed drying zone.
15. The process of claim 2 wherein a first combustible mixture of air and fuel gas is burned to supply hot drying gas for first said drying zone; and the iiuidizing drying gas fed into said fluidized bed drying zone is formed by burning a second combustible mixture of air and fuel gas; and including the steps of sensing the temperature of the effluent gas from last said drying zone; regulating the rate of flow of said fuel gas in said second mixture so as to obtain a predetermined effluent gas temperature; sensing the ow rate of fuel gas in said second mixture; and regulating the rate of ow of fuel in said rst mixture in response to the sensed ilow rate so as to proportion the drying loads in said drying zones.
16. The process of claim 2 wherein rst said drying zone is heated by burner means supplied with a stream of fuel gas and with air; and the iuidizing drying gas fed into second said drying zone is formed by burning a mixture of air and fuel gas; and including the steps of sensing the temperature of the efluent gas from second said drying zone; regulating the rate of ow of said mixture so as to maintain a predetermined eluent gas ternperature; sensing the flow rate of said mixture; and regulating the flow rate of fuel to said burner means in response to the sensed flow rate so as to proportion the drying loads in said drying zones.
17. The process of claim 2 wherein rst said drying zone is heated by burner means supplied with a steam of fuel gas and with air; and the fluidizing drying gas fed into second said drying zone is formed by burning a mixture of air and fuel gas; and including tbe steps of sensing the temperature of the efuent gas from second said drying zone; and regulating the rate of flow of fuel to said burner means so as to maintain a predetermined gas temperature in the eiuent from second said zone.
18. A process for drying Wet pellets of carbon black which comprises maintaining said pellets in a relatively deep and narrow uidized bed in a hot uidizing and drying gas in a drying zone so as to ydry same to a moisture content below about l weight percent and cause the dried pellets to rise to the top of said bed; passing the dried pellets from the upper section of said bed to a treating zone and maintaining same in a relatively deep and narrow liuidized bed in a hot treating gas therein; passing treated pellets from an upper section of said treating zone to a cooling zone and maintaining same in a luidized bed in a cooling gas therein; utilizing as said cooling gas `a mixture of air and effluent drying gas from said drying zone; utilizing as said treating gas mixture of effluent gas from said cooling zone and hot combustion gas; and utilizing as said drying gas the effluent gas from said treating zone.
19. The process of claim 18 wherein the temperature of the pellets in the uppermost section of the drying zone is maintained in the range of 150 to 300 F., the pellets in the treating zone are treated at a temperature in the range of 500 to 1200" F., and the pellets are cooled to below 400 F. in the cooling zone.
References Cited bythe Examiner UNITED STATES PATENTS 2,259,697 10/1941 Vogel-Jorgensen 11G- 106 2,520,637 8/1950 Henwood 263-21 2,529,366 11/1950 Bauer 263-21 2,638,684 5/1953 Jukkola 263-21 2,843,942 7/1958 Whitsel, Ir. 34-10 2,909,133 10/1959 Gordon 110--104 2,956,347 10/1960 Gordon 34-10 3,028,681 4/1962 Jorman et al. 34-57 3,073,751 1/1963 Gerin-et al 202-26 WILLIAM F. ODEA, Acting Primary Examiner.
NORMAN YUDKOFF, JOHN I. CAMBY, Examiners.