US1366458A

US1366458A - Method of calcining carbon for electrodes

Info

Publication number: US1366458A
Application number: US298570A
Authority: US
Inventors: Hoopes William
Original assignee: Aluminum Company of America
Current assignee: Howmet Aerospace Inc
Priority date: 1919-05-20
Filing date: 1919-05-20
Publication date: 1921-01-25
Anticipated expiration: 1938-01-25

Description

W. HOOPES. METHOD OF CALCINING CARBON FOR ELECTRODES. APPLICATION FILED MAY 20. 1919.

WITNESSES Patented Jan 25,1921,

'3'5 as compared-with prior-calclnlng processes.

matter, and which is especially adapted for UNITED. STATES"? PQ'ATENT OFFICE.

WILLIAM nooriis, or QLPITTSFURGH,PENNSYLVANIA, VASSIGNOR TQ ALUMINUM COMPANY or AMERICA, or PITTSBUBGH, rENnsYLv mA, A CORPbRA IO OI PENNSYLVANIA.

'. '1,3ce,a5s.

' Application filed May 20,

tion.

and as nearly as possible free from volatile I the manufacture of carbon electrodes of high purity and dense structure. The invention relates particularly to the continu ous calcination of coke by heating the same by an electric current passing through the coke, and the process will be described in its H application tothis particular way of heating the coke, although certain features there'- of have beneficial effect irrespective of the manner in which the heat is applied to the coke. I

The object of the invention is to provide a process for the continuous calcining of coke in a manner to produce a more uniform product than has been obtained by prior continuous calcining processes; which.

.- of prior continuous electrical processes; and

-when the heat'is applied electrically can be carried out more regularly and without the variations, fluctuations and interruptions in the current which have been characteristic one by whichthe consumption of electric or other heating energy is-Very greatly reduced For the attainment of the .jforegoingobin utilizing the heat of the finished calcined product, coke, for preheating the raw or green coke'being supplied in a continuous process, preferably. by passing a. stream of gas through the coke being treated from the 1 hot or calcined side thereof to the cold or raw side thereof. Such gas absorbs the heat from the calcined coke, thus cooling the latter, and prevents over-heating the coke at I any one point bytransferring heat by convection from the hotter to the cooler portions of the coke body being treated. The

heated gas gives off its heat, or a portion ,thereof,.to. the raw coke, thus preheating I the latter andthereby reducing the amount of heat energy which must be supplied to Specification 01 Letters Batent.

The invention relates to a process of calcining coke to produce. coke .of high quality rim-non or Clementine cannon 110R ELECTRODES.

Patented at. 25, 19.21. 1919. Serial. No. 298,570.

thoroughly calcine the-coke; and, in the case of the heat being supplied by'an' electrical current traversing the coke body, rendering the raw coke electrically conductive to there by overcomeyariations,fluctuations or interruptions in the heating current.

The process is particularly adapted for the production of coke for use in the manufacture of high grade carbon electrodes, such, for instance, as are used in electric reducing or metallurgical processes. ,Such carbon electrodes of high quality require a carbon ofhigh purity. and one as nearly as possible free from contained volatile matter. The-principal source of such pure coke is the well known petroleum coke resulting from the distillation of petroleum. This from the oil stills contains before the coke is suitable for the manufacture of high grade carbon electrodes. This volatile matter is driven off by heating the coke to temperatures in the neighborhood of 1100 C. and in a manner to prevent contact of the hot coke with the air or other gases which would cause oxidation.

Several methods have heretofore been employed for calcining such coke of which it is necessary to-consider only the continuous electrical process, in which the heat is developed within the charge itself by assing an electric current therethrough. everal difli'culties have been encountered in attempting to calcine coke bythis continuous electrical process. One of these difficulties is due to the negative temperature co-eflicient of resistance which is-an inherent property of the raw coke, as a resultof which that portion of the charge through which the electric current first establishes a path-is heated thereby, the resistance of this path decreasing as the temperature rises andtthis in turn causing more current to follow the 1 original path, thus causing further heating with the result that the concentration of current and the rise oftemperature along this been removed orreducedto lo'w proportions connection of the terminals 6 of the heating the material is a very poor conductor of electricity and does not become a good conductor until it has been heated. Consequently the supply of comparatively cold raw coke in a continuous operation has a tendency to break the circuit where the comparatively cold coke surrounds or is in contact with theelectrode. Consequently it has been difiicult to carry on a continuous process with coke containing volatile matter with smooth and regular operation and without great variations in the current and even frequent interruptions of it.

,The present method overcomes these difii-' culties and, furthermore, provides a method in which the consumption of electrical energy necessary to carry on the operation is very greatly reduced as compared with prior methods, this being due, as before stated, to utilizing the heat of the finished coke for heating the raw coke, so that when the latter enters the zone of the electric circuit it is already a comparatively good conductor of current.

Various forms of apparatus may be used for carrying out this process, the accompanying drawings showing diagrammatically in partial section one arrangement of apparatus suitable for practising the process and which has been found efiicient in practical operation.

conveniently connecting said sections to-' gether. Between the flanges of the adjacent sections is inserted a layer or insulating material 31 which may be asbestos, mica or other suitable insulating material not readily affected by heat, and which serves to electrically separate the sections from each other. The current is led into the'top sec tion and out of the bottom section through copper flanges 5"provided with means for the circuit. These copper flanges are conductively secured to the flanges of the shell section. either by bolting, riveting or in any other well known way. The lower shell section and its conducting flange rem a layer of brick 7 or other insulating material," which inturn is supported by the base 8 of the furnace. The interior of the shell along its entire length is lined with material of varying compositions for the purpose ofconfining the heat'to the center of the shaft, the

diameter of the shell and the thickness of the lining being such as to leave a shaft of any desired diameter through which the coke to be calcined passes. The lower and u per sections of the shell are lined,'at least or a portion of their length, with a carbon lining 9, preferably baked in place and making electrical contact with the metal shell so that the current can pass through the shell and through this conductive-carbon lining into the cokewhich is in contact therewith. The remainder of the lining is composed of fire brick 10, or other heat resisting insulating material. As shown, the entire central section and a portion of each ofthe top and bottom sections adjacent to the central sec tion are provided withthis insulating lining, which is maintained bythewater jacket at a temperature low enough that it does not become electrically conductive, and there-' in the shaft from the central shell section.

Consequently the current passes into the top shell section, thence through the carbon lining therein, thence into the column of coke, thence downwardly through the column of coke to the carbon lining of the lower sec tion, thence to the metal shell surrounding the latter and to the other terminal of the electrical circuit. j,

j The top of the furnace is closed b a flange 11, to which is connected a vertical pipe 12, to the top of which is connecting feeding means 13 arranged to permit a regular entry of the coke into the furnace without permitting the entry of air thereto or the escape of gases therefrom. Above this isa hopper I 14 to which the raw coke is supplied to be fed into the furnace. The bottom 8 of the furnace is provided with a hole at least as large as the size. of the shaft through which the calcined coke passes. Below this discharge orifice is mounted a suitable extractor 15, shown as of the reciprocating type, by means of which the discharge of coke through'the orifice can be regulated. The casing of this extractor is secured to the base 8 of the furnace and is provided with ports 16 for the entry of as for a purpose hereinafter described. he extractor serves to drop the coke regularly in a closed hopper 17, the bottom of which is provided with a valve 18, to .permit withdrawal of the coke.

In order to preheat the raw coke and utilize the heat of the finished coke for this purpose, gas is introduced throu h the gas orts 16 and caused to pass u war ly-throug the column of coke in the urnace, thus absorbing heat from the finished coke and cooling it to such extent that it will not ignite when it comes into contact with the air, and which gas in passing upwardly through the column of-raw coke heats the latter and renders'it electrically conductive by the time that it enters the upper portion of the electric circuit through the furnace. Gas for this purquality, this distilled oil gas is'preferably used forthispurpose. To this end the pipe 12 is provided with a side outlet 19 through which the gas distilled from the coke in the furnace passes and is thence carried by pipe 20 in succession through a washer 21 and scrubber 22 for the purpose of .cleaning said gas and also cooling it. The cleaned or cooled gas'is led from the scrubber through pipe 23 which is provided with two branches, one of which leads to the pump 24 while the other branch 25 is for the purpose of removing from the system the excess gas. As shown this branch 25, controlled by valve 26, for regulating the rate of discharge of the gas, is connected to a pipe 27 which extends into a water seal 28, whence the excess gas is withdrawn from the system and'in a manner to prevent the entry of air into the system. The discharge side of the pump 24 is connected by

pipes

29 and 30 to the ports 16 above mentioned in the extractor casing, preferably entering said casing tangentially as shown; whence the gas circulated by the pump enters the cokecolumn in the furnace.

In carrying out the process by the above described apparatus the shaft of the furnace is first filled with calcined coke which is a conductor even when cold. 'The current-is then turned on, and due to the resistance of the coke column the electrical energy of the current is converted into heat thus preliminarily heating the furnace. When the temperature of the furnace has been raised to the proper operating temperature and suflicient time has been allowed for;the combination of all of the oxygen in theair con-- tainedin the system with the hot coke, the pump is started and gas circulation begins. The extractor 15 and coke feeder 13 are then started and raw coke is fed into the shaft to replace the calcined coke being withdrawn. The gas forced into the shaft from the pump rising through the hot coke column absorbs heat from the latter, and when it passes through the raw coke gives up to the latter a portion of its heat, thus preheating the latter and driving off a portion of the volatile matter contained therein and brings it to such temperature and composition that it becomes electrically conductive. As a consequence, by the-time this raw coke getsdown into the electrical circuit it is already a good conductor of current and consequently there are no fluctuations or. interruptions of the circuit. As" the withdrawal and feeding proceed, raw coke which has already been partially calcined comes into contact-with the upper. electrode 9 and he gins to form a portion of the electric circuit,

and its calcination is completed by the heat- 7 ing by the electric current as the coke passes downwardly through the furnace. As the withdrawal and feeding continues, the en-.

tire original content of the furnace is displaced andis replaced by raw coke, which is continuously calcined on its downward movement through the furnace. The rate of feeding the coke and therinput of the electrical energy are so proportioned that the calcination of. the coke is complete before it leaves the lower electrode.

The cold gas entering through the ports 16 and passing upwardly through the coke column should be sufiicient in quantity to completely cool the outgoing coke -to approximately the temperature of the entering gas which-is so low that the coke will not ignite when it gets into the air. The gas as it passes upwardly through the fur- 'nace attains approximately the maximum Either hydrogen or nitrogen would be a suitable gas, but for economy, and since the gaseous portion of the volatile matter resulting from the calcining of the coke, is a suitable gas it is preferably used. The gas passing through the furnace should be of suflicient quantity to overcome any tendency to concentration ofcurrent and heat in any particular section of the charge by absorbing the heat from any over-heated portion and transferring it to some cooler portion of. the charge. The volume of gas which must be discharged from the system is, of "course, the volume necessarily" enerated during-the calcining operation, an the volume which is forced into the bottom of the furnace and circulated through the system bears no relation to the amount of gas generated and can be made any desired quantity as may be found to be most suitable. The discharged gas can be used for fuel or other purposes, and since (after the system is once started) it is the total volume necess'arily generated during the calcining operaand conduction must be supplied and these are supplied by the energy of the electrical current; but the amount of such energy required for the calcination of a unit of coke by this process is much less than that required where the recuperation described is not made use of. i

The proportions of gas, coke and electrical energy can be made such as to permit both the gas and the coke to be discharged at comparatively low temperatures, which is the condition of maximum elliciency. At this low temperature the gases contain the volatile products of the coke in solid, liquid or gaseous form, depending on the physical nature of the variety of compounds driven off. The washer'and scrubber remove from the gas .as much of the entrained matter as can be/removed with apparatus of this kind and also cool the gas so that the portion of that gas which is returned to the furnace is substantially cold and will effectively cool the finished coke to such temperature that it will not ignite when it comes in contact with the air. The gas distilled from the coke is composed principally of hydrogen and hydro-carbons. That portion of the hydrocarbons contained in the gas which is returned to the furnace is largely decomposedthe electric circuit, and results in a more uniform product, all portions of the coke column being,'through the medium of the hot gas passing through it, maintained at substantially the same temperature and the same condition of conductivity.

lVhile theform of furnace illustrated is the preferable one, the process is not limited to the use of such furnace. Many other forms of furnace can obviously be used for the same purpose. For instance, it is possible to use a shell lined entirely with fire brick and in which the electrodes are placed at the center of the mass of coke at the two ends of the coke column, and one or both of said electrodes being completely insulated for the lining, which is a form of furnace utilized in previous methods of ca-lcination. The construction illustrated has the advantage that the electrodes are external to the column of coke and therefore there is nothing to obstruct the free passage of the coke from the top to the bottom of the furnace.

While the process is of particular value in connection with the electrical heating of coke in a system in which the coke to be' calcined forms a part of the electric circuit, it is not restricted thereto, as certain features thereof are useful in connection with the calcining of coke no matter how the heat is applied. For instance, the function of the gas forced through the column to prevent overheating of, any portion of the cross section of the column by furnishing heat by convection from the hotter to the cooler portions of the column, and for the purpose of utilizing the heat of the finished coke for preheating the raw coke and thus reducing the amount of heat necessary for ca-lcinin' the coke, can be applied to and is usefu with calciners in which the heat is applied externally to the column, such as by applying heat to the exterior of a shaft furnace,

by means of a suitable fuel heated chamber,

as in the case of the well known vertical tinuously and which retorts are heated externally by burning a mixture of gas and air. These retorts are lined with silica brick and the heat which serves to calcine the coke must pass through such brick walls, which, as is well known, are poor conductors of heat. If to such retorts there is added the arrangement for introducing gas at the bottom, thus abstracting heat from the finished coke and preheating the incoming coke, the quantity of heat which must penehate the walls of the furnace to calcine a given quantity of coke will be very much reduced; or with the same amount of heat a larger amount of coke can be calcined, thus permitting a more rapid rate of passing the coke through the retort and thus increasing its capacity. Furthermore, the passage of the gas through such retort will prevent the overheating of the coke at any one portion thereof and the underheating of any other portion thereof, thus tending to a more uniform product.

The apparatus illustrated is claimed in an application of even date herewith, Serial No. 298,569

I claim:

1. The process of calcining coke, consisting in supplying raw coke to the top of a column thereof of substantially uniform cross-sectional area from top to bottom, withdrawing calcined. coke from the bottom of said column, passing an electric current through an intermediate section of said column of coke, and simultaneously forcing through the entire column a current of inert gas to uniformly cool the calcined coke in the lower section, to uniformly distribute the heat in the intermediate section, and to uniformly preheat the coke in the upper section of the column.

ing in supplying raw coke to the top of a column thereof of substantially uniform cross-sectional area from top to bottom, withdrawing calcined coke from the bottom of said column, passing an electric current through said column of coke, Withdrawing the gas from the top of the column, cleaning and cooling said gas, and" returning a portion of said gas to the bottom of the column, whereby to cool the calcined coke, heat the gas and cause the gas to preheat the raw coke. v

3. The process of calcining coke, consisting in supplying raw coke to the top of a column thereof of substantially uniform cross-sectional area from top to bottom,

Withdrawing calcined coke from the bottom of said column, applying heat to said column, Withdrawing from the top of the column the gas generated by the heating of 20 the coke, cleaning and cooling said gas, and returning a portion of said gas to the bottom of the column, whereby to cool the'calcined coke, equalize the temperature throughout the cross-section of the column, and heat the 25 raw coke entering the column.

In testimony whereof I have hereunto set