US2200717A - Process of coking pitch - Google Patents

Description

ALP. MEYER PROCESS FOR COKING FITCH Filed AU. 17, 1938 May 14, 1940.

2 sheets-sheetv 1 mwN A. P. MEYER PRGCESSvFOR COKINGv FITCH May 14, 1940.

2 Sheets-'Sheet 2` Filed Aug. `157, 1938 .N g ,m1

Patentecll May 14, 1940 OFFICE PRocEss` or coKlNG rl'rcn Albert P. Meyer, Pittsburgh, Pa., assignor to Pittsburgh Coke & Iron Company, Pittsburgh, Pa., a corporation ol' Pennsylvania Application lAugust 17, 1938, Serial` No. 225,438

` (ciauz-19) i l a utilized inthe present invention. Further appli- 2 Claims.

This invention relates to coking pitch; and it comprises a method of making substantially pure hydrogen-free carbon in'friable form suitable i'or electrode use'wherein a body of molten 5 coal tar pitch is established as a long narrow pool not. over 30 inches in Width and is subjected to destructive distillation by the action of hot gaseous products of combustion passing upwardly therethrough until the residual content of volam tilizable matteris removed and until the liquid pitch changes to a loose, spongy, vesicular body of carbon and shrinks away from the walls of the containing chamber, and continuing passage of the hot combustion products in contact with the body until a carbon is obtained containing not more than 1 per cent volatile matter (hydrocarbons) all as more fully hereinafter set forth and as claimed.

The present invention is directed to making a zo pure carbon suitable for electrodes, a product 30 in a cupola or blast furnace), are not required or desired. In a carbon to be comminuted and reshaped as electrodes, high mechanical strength is not so desirable as a friable, readily comminuted preparation.

`In the present invention coal tar pitch. is used as the immediate source material for pure carbon; pitch being the residue in the distillation of i tar for recovery of coal tar oils,`light and heavy, cresols, creosote, etc. The pitch can be obtained 4o as the residue from ordinary distillation of tar in any of the usual Ways; or if desired the pitch can be produced from tar in the same apparatus later used for carbonizing the pitch, in continuous successive operations. In another and com- 45 panion application Ser. No. 225,439 I have described and claimed a method in which both distillation and carbonization are successively efiected in the same apparatus.`

Coal tar in its original state contains a considerable amount of volatile hydrocarbons distillable as such, which are commercially worth while. 'Ihese may be removed and recovered by heating the tar to a temperature of the order of 500 to 700 F., the residue being reduced to hard pitch.` Pitch at a temperature of this, order is cation ofV heat to, the pitch effects destructive distillation. As a matter of `fact, simple distillation and destructive distillation overlap, but the distillation which occurs at temperatures lower than the aforesaid range of temperatures in the ordinary types of tar still is predominantly'simple distillation, while that occurring at higher tem-` peratures is predominantly destructive distillation. Up to acertaln point distillation is endo'- `thermic, but as the temperature of the pitch rises to some point above 1000 F. with destructive distillation, the material passes through a definitely exothermic stage and a self-coking effect is noticeable.

. I have observed that processes of this character in which destructive distillation and coking occur ordinarily yield a product which is more aptly described as a "semi-coke than as a true coke;

a material having a denite cell structure but containing a substantial content of volatile matter, usually in excess of 3 per cent. Carbonization has not been completed. I dnd that for my i purposes in order to complete carbonization and destructive distillation, with removal of volatile matter down to 1 per cent or less in the nal product, `finishing temperatures substantially in excess of 1500o F., and preferably of the order of 1800" F., are required. At such temperaturesr all of the hydrocarbons present tend to break down to free carbon and hydrogen. The action in this nal stage is neither markedly endotherrnic nor exothermic, but it does require application of sufficient heat to maintain temperatures of the order noted for suiilcient time to complete the action, that is, a soaking heat to insure that all portions of the mass of residue 'are subjected to such temperatures. However, if the carbonaceousmass is disposed in such fashion that the center of the mass is located at a considerable distance-from the point of application of heat, it is impossible as a practical matter to reduce the average volatile matter content of the mass to a sufficiently low point, even when the wallsv of the retort are maintained at the aforesaid high temperature. A number of processes have been p roposed and utilized in the past for making coke from coal tar; mostly for metallurgical purposes.,

signed for the `manufacture of high tenlperaturey` lay-product coke from coal. As a practicalmatter, these ovens are extremely expensivevand 2 o y i serious diilicultles are encountered in their use, when attempting to coke pitch, principally due to foaming during the coking operation. All at' tempts to overcome these difliculties result, in one way or another, in reducing the efficiency of the operation from .other standpoints. In .the presentV process naliconversion of thepitch into an open texturedvpuifed'up solidiedmass is desired and this foaming effect is utilized. Among the objects achieved by my inventio is the provision of a process forreducing coal tar pitch to electrode carboncontaining 1. per, cent volatile matter or less. inq a unitary operation, with a minimum of mechanical dizlllculties, with high yields of products, and in a reasonably short operating period.

Additional operative .advantages and: improvements obtained in accordance with my invention i will alsofbe evident from' the' following descripprovided with vertical doors ateach end, for

pushing the finished coke horizontally out of the ,ovenl in a manner similar to the manner in which coke is removed from by-product coke ovens operating on coal. Each chamberl is provided with a plurality of inlets near the floor thereof, for introducing hot gases, which in the ordinary instance will comprise gases produced by the combustion of solid, liquid or gaseous fuel. 4Means are provided for leading the exit gases and vapors to sultablecondensers, heat exchangers, coolers, and the like, and ultimately to an exhaust fan capable of maintaining a substantial vacuum.

In the operation of the apparatus, coal tar pitch is introduced into the retort chamber in -suillcient amount to lill the chamber to about one-third to one-half of its capacity, that is, to a depth between 3 and 8 feet. The pitch isintroduced in a fluid or molten condition, and preferably at a temperaturey ofk from 500 to 700 F. The'pitch may be introduced at a lower temperature in some cases, but in such event the. oven `should be preheated in order to avoid chilling 55.

the mass of pitch to a solid state. Ifdesired the pitch can be produced in situ by distillation of f tar in the retort chamber, as described below.

`IfIot gases of combustion, as free of oxygen as .possible, are then bubbled through the liquid charge under a vacuum. These gases not only `serve to supply heat but also cause free.evapora tion and, under. the influenceV of the applied vacuum, effectively,v cause` the entire mass of the charge to` be subjected to pressures below atmospheric. `'Ilie'gases reaching the upper level (of the chargeotcgether with vapors ofl volatile matter evaporated thereby, or produced by dey structivedistillation of the charge, are .passed through a condenser of suitable type. Oils thus condensed are valuable as by-products. The

cooled gases then pass from the condenser to an .exhaust fanr operated to `create a rather high suction; say, about 14 inches (water) at the top of the charge in the oven.

During the initial stage of the carbonizlng operation, the heating gases may be supplied at a temperature of the order of 1400 to 1600 F.

But in any event, the temperature of the heating gases should be gradually increased to around 1800 F. Destructive distillation begins almost immediately and the ltemperature of the charge risesfrapidly to a point usually a littleabove 1100 F. At this point there is usually a sudden drop in temperature to around 1000 F. and there appears to be a-change of phase in thel mass of vthe material being carbonized; at this point the `transition from a body ofJ liquid to a more or less solid material occurs. y

Immediately following the comparatively small drop in temperature mentioned there is ordinarily a very sharp rise in temperature, due to exothermic reaction. This rise is so marked that in some cases the temperature of the charge may actually exceed that of 4vthe heating gases. At this point the charge tends to be quite reactive with oxygen and it is especially desirable to control the amount lof oxygen in the heating gases Very closely, in order to prevent loss of material through oxidation or combustion. In any event, the ilowof hot gases is continued until the entire mass of the charge is brought to a temperature substantially in excess of 1500a F., and preferably of the order of 1800 F.. and until the average amount of volatile matter in the charge is reduced to 1 per cent or less.

With a charge not more than 30 inches thick, the time required for this portion of the operation is not excessive, and due t'o the fact that the coke is of cellular and porous structure, there is an effective penetration of heat throughout the mass, although a considerable portion of the hot gases at this stage undoubtedly iiows between the carbonaceous mass and the verticalwalls of the oven. In fact, in some cases the exothermic action which takes place after the change of phase referred to above is so marked, and the temperature of the charge rises so rapidly to a high point that the finishing or calcining period can be reduced to a minimumof around thirty minutes. The amount of gas necessary to pass through the retort at thisrstage is not excessive, and there is little or no condensable vapor in the exit gases. Consequently, it is unnecessary to pass the exit gases at this stage of the operation through the condenser used during the earlier stages; these exit gases may 'conveniently be employed for preheating another retort of the same type, or` for preheating thev charge or the fuel or air used in producing the gases of combustion, or they may be employed for the purpose of distilling coal tar to pitch suitable 'for charging into the operation.

I have found that, in a retort of the character indicated, wherein carbonization is effected by supplying hot gases directly to the mass of pitch being coked, the foaming difculties encountered in most pitch coking operations are avoided, presumably because the convective distillation effect of these gases causes constituents which would otherwise cause foaming to be removed more or less gradually insteadof being liberated during a comparatively short period. However, during the destructive distillation the charge usually puffs up to some extent and becomes for a time a more or less vesicular doughy mass, usually exceeding lthe volume of the original pitch charge. As the operation progresses farther and the volatile matter of the final product falls to 1 per cent or less, shrinkage takes place, the final volume vof the charge being ordinarily about equal to or After the operation has been completed, .the

now of gases is discontinued,` the doors at-the ends of the retorts are removed, and the coke is discharged from the oven or retort by pushing it horizontally with apparatus designed yfor that purpose. The doors are then replaced, and, where necessary, after preheating to around 500 to 700 F., the oven is then ready to receive a fresh charge and the operation is repeated.

'I'he following description, given in conjunction with the drawings illustratingand forming part of this specification, will serve to explain and exemplify my` invention in further detail. In these rdrawings, i

Fig. l is a vertical cross-sectional view of a coke oven suitable for use in my invention;

Fig. 2 is a horizontal sectional view of the same oven taken alon'g the lines 2--2 of Fig. 1; and Fig. 3 is a more or less diagrammatic view of the oven shown in Figs. 1 and 2, in association with auxiliary apparatus employed in carrying out the process of my invention.

Similar reference numerals designate similar parts in the several views of the drawings. l

As shown in Figs. 1, 2 and 3, I provide a coking retort oven comprising a refractory structure yIll so constituted as to provide ,a retort space of rectangular shape, having vertically disposed doors I I at the ends thereof and suitable supporting framework I2. As has been indicated hereinabove, the dimensions of the retort space with in the refractory structure I may vary to some extent, but the retort illustrated in the drawings is one having internal dimensions as follows: length, 8 feet; height, 10 feet; width (at discharge end), 20 inches; width (at pusher end), 16 inches. A series of conduits or tuyres I3 is provided in the bottom portion of each of the vertical walls of the structure I0, for admitting gases of combustion. As shown in the drawings, the tuyres in one of the vertical walls are preferably staggered with respect tothe tuyres in the opposite wall; each tuyre lies opposite to a point about midway between adjacent tuyres in the opposite wall. The tuyres I3 are in turn connected to horizontal ues I4 in such a manner as to provide for easy access and cleaning of the tuyres I3. The fiues I4 are in turn connected through vertical risers I5 to a nue manifold structure I6 which is supplied with hot gaseous products of combustion through a conduit I1 from a combustion cham-ber I8 having a fuel burner I9. All of these conduits and tuyres are lined with refractory material for protection.

Liqueed pitch, preferably at a temperature of 500 to 700 F., is introduced vinto the retort through a line having a'valve 2I and corn-v municating with a source of supply (not shown) of the charge, such as a tar still. Or if desired the pitch can be produced directly in the retort by distillation of tar, as described below.

At the top of each retort there is provided one or more off-take fiues 22 having a removable cap or stack valve 23 and communicating through a crossover ue 24 and a down-comer 25 to a tar trap 26 having a drain-21.

From the tar trap 26 the gases and vapors from the interior of the retort pass through a pipe or flue 29 into a scrubber 30, the interior of which is provided with tile packing 3| or other suitable gas-and-liquid-contact material. Condensate withdrawn from the bottom of the scrubber 30 iswlthdrawn therefrom through a valved pipe 32 leading to a pump 33. A portion of this condensate is recirculated through a line 34', an indirect cooler 35 and aline 36 to a spray or other distributing device 31 located in the top of the scrubber 30. Another portion is pumped through a branch line 36 into the down-comer- 25. Excess ,condensate is removed through a valved line 39 and sent to, storage.

The cooled gases leaving the scrubber 30 pass through a conduit 40 tcan exhaustor or vacuum pump 4I which in turn delivers them through a conduit 42 to`an exhaustv stack 43 or, where desired, into suitable heat exchangers or preheating devices. Any excess liquid collecting in the bottom of the exhaust stack 43 is removed through a line 44 and passes to a suitable storage vessel 45. I also provide a valved line 46 for introducing` a portion of the condensate into the conduit 40.

The operationI of this apparatus will be clear from the description given hereinabove, pitch being charged into the retort structure I0. and heated. internally by means of hot gases produced in the combustion chamber I8, and. the temperature of the gases being regulated in accordance with the foregoing description.

After the operation has been completed, and the charge is reduced to the desired low volatile content, the doors II at the ends of the retort structure are removed, and the coke is pushed out of the oven by means of a pusher 50, similar to those used in connection with by-product coke ovens commonly used for coking coal.

Where desired, a plurality of retorts similar to those described and illustrated hereinabove may be employed, it being preferable to build these in the form of a battery of retorts. In such case provision is, of course, made for operating the retorts alternately or ina series of scheduled operations, and for connecting and disconnecting the exhaustor 4I to such oven or ovens as may be in operation at any given time.

As stated, if desired the pitch can be made in situ from coal tar, tar being introduced into chamber I0 through conduit 20 in amount sulicient to fill the chamber about two-thirds full. The tar is heated by means of hot gases from the combustion chamber I8. Distillation takes place and the distillate is condensed in tar trap 26 and scrubber 30. In due course the tar becomes con--4 verted into pitch and the pitch is then carbonized by destructive distillation in the procedure explained above.

While my invention has been described hereinabove with reference to Various illustrative details of apparatus and operation, it will be understood by those skilled in the art that my in- Y Vention in its broadest aspects is not limited to zontally elongated substantially rectangular body of. molten pitch not over 30 inches in Width, introducing gaseous products of combustion entering at a temperature of 14001600 F. into said body at a plurality of points along its length and near the bottom thereof while maintaining a partial vacuum thereabove, gradually raising the temperature of the combustion gases to about 1800 F. until the pitch body becomes a vesicular solidresidue and continuing a flow of the hot gases through and in contact with the solid residue until it reaches -a temperature exceeding 1500? F.1iand'solid carbon' is 'produced having a. volatile matter content less than 1 per cent by weight. v

2. A methodof making substantially pure carbon fromcoal tar pitchwhich comprises establshing a horizontallyv and vertically/elongated body of molten pitch not over 30 inches in width, introducing gaseous products of combustion entering at a temperature of 1400 to 1600 F.1into i `e1 per cent by weight.l

atoom? sala body al. a plurality of points along its length near the bottom thereof while maintaining a. partial.I .vacuumthereabov'e, gradually raising thetemperature of the combustion gases until the pitch body becomes-va vesicular residuev and contlnuing a fiow'of 'hot gases along and intcontalctl withthe solid residue until it reaches a temperature exceeding 1500" F. and solid carbon is produced having a; volatile matter content less than l ALBERT P. MEYER.

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