US1341437A - Method of distillation - Google Patents

Description

E. E. PERSHALL.

METHOD OF DISTILLATION.

APPLICATION FILED FEB. 20. 1918.

Pamnted May 2 5, 1920.

3 SHEETS-SHEET I.

E. E. PERSHALL.

METHOD OF DISTILLATION.

APPLICATION FILED FEB. 20, 1918.

1,341,437, I Patentd May 25,192

3 SHEETSSHEET 2.

E. E. PERSHALL.

METHOD OF DISTILLATION.

APPLICATION FILED FEB. 20, 1918.

1,341,437. I Patented May25, 1920.

Y3 SHEETSSHEET 3.

- EDWARD E, PERSHALL, OF ST. LOUIS, MISSOURI.

METHOD OF DISTILLA'IION.

Application filed February 20, 1918.

To all whom it may concern:

Be it known that I, EDWARD E. PERSHALL, a citizen of the United States, and a resident of St. Louis, in the State of Missouri, have invented certain new and useful Improvements in Methods of Distillation, of which the following is a specification.

My invention relates broadly to the distillation of hydrocarbon materials. More specifically it relates to the distillation of hydrocarbon pitches and tars so as to obtain a residue of coke. Its primary object is to obtain a relatively high percentage of distillates, and especially a relatively high percentage of the high-boiling, high specific gravity distillates, which are the most valuable elements of the-materials enumerated, and to obtain such latter distillates having distinctive properties in that they are substantially unchanged from their natural condition; and also to obtain a superior quality of coke. A specific object is to obtain substantially complete fractionation of distillates whereby substantially the highest percentage of the valuable heavy oils is obtained in the proportions in which they existed in the hydrocarbon mass before-distillation was begun, and a residuum of coke which is substantially the smallest quantity obtainable, which is substantially free of all volatile bituminous compounds, which is notably high in fixed carbon, and which, when burned, leaves but a small percentage of ash.

- saving in fuel as well as reducing the hith- A further specific object is to effect substantially complete distillation with substantially a minimum of temperature and quantity of heat, thus effecting a notable erto abnormal deterioration of the apparatus employed due to excessive heat.

Other objects and advantages of the present improvements will appear at varibus places hereinafter.

By fractionation of the distillates, or fractional distillation, I mean the passing over of the vapors of volatilization according to the specific gra'vities and boiling points of the several products when condensed, one

after the other in the natural order, without thesubstantial destruction of these several vapors after having been formed. This term is distinguished from destructive distillation, which comprises the decomposition or cracking of the vapors, and which're-l Specification of Letters Patent.

Patented May 25-, 1920.

Serial No. 218,247.

sults first, fromthe impingement of the vapors upon a surface heated greatly beyond the temperature at which the vapors were formed, and, secondly, from the condensation of the vapors and the falling back of the liquid upon the highly heated surface of the mass, such vapors or liquid thereupon decomposing partially into lighter and partially into heavier substances.

In one aspect of my invention the hydrocarbon material subjected to complete distillation according to the present method and apparatus is pitch, of various consisten cies, which pitch maybe the product of the partial distillation of coal-gas tar, watergas tar, coke-oven tar, blast furnace tar, wood tar, or any other similar material. In another aspect the invention is directed to the complete distillation of such tars into and through the pitch state to coke: as one continuous operation.

These improvements will be explainedfin connection with the accompanying drawpresent form of still are largely in its provision of substantial uniformity of heat distri'bution throughout the mass, the saving-0f fuel, the employment of relatively low temperatures, the avoidance of cracking or decomposition, theavoidance of excessive deterioration of the apparatus itself, ease and safety of operation, rapidity 'of operation, and, generally, in saving cost while obtaining the most valuable distillates in relatively large quantities.

The apparatus illustrated includes an internally and externally fired still. Preferably at least two fines for the heat pass longitudinally through the interior of the still, where the still is of the shape and proportions shown, and which, in my practice, has su'ch'capacity as to contain a working charge of approximately eight thousand gallonsof tar. 'For a still of greater capaity the number or size of such flues may be increased, and in a relatively small still a single flue will suflice. The desideratum in equally subjectedtothe distilling heat, or, in other words, substantially to equalize the transmission of heat throughout the mass. In my practice the tubular retort is approximately sixteen feet long and ten and onehalf feet in diameter, and the two flues are respectively two feet in diameter, and they extend from end to end of the retort. Their arrangement to provide the desired heating result and also access for cleaning out the residuum is well illustrated in the drawings, which are substantially true to scale. Steam is admitted preferably at the bottom and distributed in fine jets from end to end of the retort. A condensing system is pro-v vided for the vapors of distillatiom'which system and the interior of the retort are preferably under a partial vacuum of various degrees of intensity, according to the amount of steam employed or the rate of volatilization, or both. Collecting tanks, preferably several of them for convenience of operation, are also employed, with suitable pipe connections, and also means for providing distilling heat. The upper portions of the retort are not in contact with the heating gases or flame.

In the-present form of still decomposition or cracking of the vapors of distillation is avoided by maintaining" the upper surfaces of the retort at a medium temperature,

and particularly one not greater than thatat which the distillation is tak'ing place;

and, in obtaining the notable advantages of' tion,and, as a further means for avoiding" or reducing the condensation, rapidly drawing away the combined oil vapors and steam through suction in the discharge pipe leading from the retort.

It is not broadly new at this time to produce coke from the complete distillatio n'of tar, the same having been done in Europe as early I believe as the middle of the nineteenth century. It is also old to employ steam or vacuum, and steam with vacuum,

in a retort during the processof such partial distillation as results in a residue of ordinary pitches; but I claim it as new to employ steam, with or without vacuum, at the time when the formation and deposition of coke or heavy residues on the bottom and takes place.

sides of the retort would otherwise take place in substantiallylarge quantites, and in continuing the use of steam until the complete formation and final hardening of the coke, thus saving the retort from destructive overheating and gaining the further advantages herein above.{and hereinafter pointed out. It is also new to heat the mass by internal and external application, and to provide for the continued flow or movement of the mass over andfabout the heated surfaces of the retort until final hardening plete distillation to maintain the upper surfaces of the retort at'a medium temperature It is also novel in such com to avoid cracking, and to employ steam,

with or without vacuum, in connection with such medium temperature of said upper surfaces. Still other features of novelty will appear from this description and in the appended claims. i

The presence of steam applied as herein pointed out from small jets into the body of the hydrocarbon mass substantially up to the time of the formation of coke has several distinct actions upon the massand upon the vapors of distillation, namely;

first, a mechanical one whereby the vapors are carried along by the steam currents to the condensing apparatus; secondly, a solvent action upon the vapors whereby the steam particles act as vehicles in carrying the vapors away, and Without changing their composition, and doing so more quickly and certainly than by the mere mechanical action next hereinabove described; thirdly, by creating a .system of partial -pressures of the vapors of distillation and of the steam, inducing volatilization at a temperature lower than the true boiling point of the hydrocarbons from which the vaporsare being produced; fourthly, the creation of currents within the mass, which currents are preferably controlled so as to cause the mass to circulate and thus cooperate in avoiding local overheatingor underheating of portions'of the mass within the still.

The foregoing four actions of the steam are utilizedby me in-the partial distilla tion of the tar down to and including the formation of pitch. Preferably the steam is not used until the lighter oils have passed over, the tendency of the steam being to condense objectionably' at the lower temper atures of the still. In obtaining'the valuable distillates of the heavier specific gravities and higher boiling points from .the pitch and in the production of coke further advantage is taken of these'four actions of the -steam mentioned, together with other actions which'l have discovered to be of great utility and which have an important bearing upon the distillates and coke, as well as upon considerations of safety to the Sixthly, the absorption of such gases, in-

a manner similar to that of the second action mentioned above;

Seventhly, the distribution of heat; Eighthly, preventing the coke from adhering tightly or cementitiously to the walls of the retort;

N inthly, giving the coke a peculiar construction characterized by relatively deep cells in substantially parallel arrangement and having relatively thin walls;

Tenthly, cooling down the mass;

'Eleventhly, molstening the mass;

Twelfthly, overcoming the partial vacuum in the retort while continuing the action of the suction creating apparatus, thereby preventing the walls of the retort from collapsing, which might occur under vacuum and. high temperature in the last stage; Thirteenthly,the final filling of the retort with steam so that. when opening the same for cleaning and air is admitted there is no danger of an explosion. In the drawings referred to Figure 1 is portion Fig. 2 is an elevation of the condensing and collecting apparatus;

Fig. 3 is a transverse vertical section, as on the line 83 of Fig. 6;

Fig. 4 is a greatly enlarged fragmentary sectional view of the steam pipe in itsrelation to the bottom of the still;

Fig. 5 is a fragmentary transverse vertical section, as on the broken line 5-5 of Fig. 6; and

Fi 6 is a vertical longitudinal section on the broken line 66 of Fig. 1.

The retort 10 in my practice is of boiler plate, is tubular, and is provided with two fiues 11 and 12 from end to end of the retort rigidly and tightly secured to the end walls according to standard practice in boiler making. The retort is suitably supported by brick side walls 14 and 15, a rear wall 16, and a front wall 17. A Dutch oven, which requires no detailed description, is

shown at 18, and the front wall19 spaced from the wall 17 7 provides a passageway 20 for the burning gases from the oven .to the fines 11 and 12 for .internal firing. The rear wall 16 is. formed to provide a passageway 21 for these gases leading downward to the heating chambers 22, 22*, defined by the bottom and lower side portions of the retort and by the layer of bricks 23 supported by the bed of ashes or other suitable material 24. The heating current passes into the chamber 22 through arched openings 25 formed in the masonry.-

Two oppositely disposed bafiie walls 28 are provided for preventing the heating currents from playing too strongly proportionately upon the side portions of the retort, or, in other words, the baffles 28 provide a pas sageway betweenthe chambers 22 and 22 effectively close to the bottom portions of the still. Thus, while the gases in the chamber 22 will exert heating effect upon the side portions of the retort they are compelled by the baflies 28 to pass substantially under the retort between the two baffles, and since this constricted opening, indicated at 30, Fig. 3, is the shortest and most direct passage-way for the gases entering through the openings 25 the efiect is that by far the greater amount of the externally applied heat is directed to the lower portions of the retort.

From the chamber 22 (Fig. 6) the heating current passes forward and upward into the lateral chambers 32 (Figs. 1 and 5) and thence upward into the transverse chamber 33, and thence into the stack 34 provided with the damper35.

The retort is provided with two top manholes and covers at 38 and 39. The pipe 40 leads to the condensing apparatus from the top of the retort. It is provided with a hand valve 41 and a vacuum safety valve 42.

The retort is provided with a safety pressure valve 43.

Steam is admitted through the pipe 45 I which terminates near the bottom of the re- "tort midway of the discharge pipe 46, the

ating in equalizing the distribution of heat.

An important feature of the construction is in the relation of the upper portion of the retort 10 to the heating current. It will be noted that the direct application of heat to the exterior walls of the retort is substantially only half-way upward from the bottom. The wall 50 (Fig. 6) protects the upper front end portion of the still from the direct action of the heat, while the wall 51 protects the upper rear end portion against becoming too cold. The upper side and the top surfaces are also bricked over by the wall 52 to protect these surfaces from the cold. The covering walls 51 and 52 have the further and important function of absorbing, conducting and retaining considerable quantities of heat from the still as a whole protects them from the outside temperature while preventing substantial radiation from these walls. It is pointed out that the walls 51 and 52 automatically exert their desired influence in thisrespect during the whole period of distillation since they naturally become hotter as the heat of the still is gradually increased to distil the heavier compounds.

. The outlet pipe structure 54 has a substantially large opening into the retort, and

pipes 55 and 56 lead from the outlet pipe 54 to the manhole chambers 38 and 39 respectively, thus providing for the rapid withdrawal of the vapors from a plurality of places along the top of the retort, centrally as well as nearer the ends. While I prefer a plurality of such withdrawal openings, the same is not strictly necessary.

For removing the coke from the still I provide a manhole and cover therefor shown at 58. A tubular extension or neck leads from the interior of the retort 10 to the manhole cover through the wall 16.

The condensing apparatus .60 is of the usual form comprising a coil of pipe in a tank of water. Two collecting cylinders 61 and 62 are arranged to take the liquid of condensation from the container, and by means of the pipe 63 the liquid is drawn off as desired. Ordinarily one tank will be used at a given time for receiving the products of distillation, suitable valves as indicated being adapted to shut off one or the other of the tanks as desired. A partial vacuum is created in the tanks 61 or 62, and conse quently in the condensing. worm 60, in the pipe 40 and in the upper portion of the retort 10, by any suitable means, such, for instance, as the steam siphon 64; connected by asuitable valve-controlled pipe system 65 to the tanks respectively.

My improved method will be described in connection with the complete distillation of refined coal tar to coke, and by refined coal tar I mean a tar produced by the removal of the lighter constituents amounting to approximately 5% of the coal tar in its crude state. The tar is introduced into the retort through any suitable pipe, not shown, or through one of the top manholes i1lustrated, to a suitable height in the retort dependent upon the water content, the free carbon content, and the amount of coke which will result from complete distillation. are variables and thbse skilled in the art can readily approximate the proper maximum charge. The minimum charge should be sufficient to cover well the flues 11 and 12. In my practice with the above-mentioned refined coal tar the average maximum chargefills the retort up to seveneighths of its capacity.

These several properties of the tar' Having closed all openings except the ipe leading to the condenser, the fire is started and distillation begins. Partial vacuum is created in the condenser and in the top portion of the still, which vacuum may suitably be equal to about two or three inches of mercury.v The process of distillation may.

well continue with or without the admission of steam until after the major portion of the distillates have been collected.

The admission of steam during the earlier stages is sometimes objectionable on account of the excess of water condensed. When, h0wever,'the specific gravity of the distillates has reached about 1.15 at a temperature of 100 F. it is to be considered that steam is being admitted in a relatively small quantity, and has as one of its functions the agitation of the mass through the formation of currents therein, which currents are preferably according to predetermined lines. Thus, in the still illustrated the steam issuing laterally from the horizontal pipe 46 causes currents to form upward along the sides of the still and over the tops of the fines 11 and 12 and downward between the fines, the currents thus being substantially around these fines. In my practice during the distillation from time to time I increaseslightly the amount of steam admitted, say every half hour, the additional steam acting to continue the currents in the gradually thickening mass. The admission of steam during the passing over of the distillates has .the further advantages of creating the system of partial pressures and the carrying away of the vapors of distillation as pointed out hereinabove.

The foregoing steps including steam and vacuum are carried on until the final stage of distillation, which is just prior to the time when the cokeis beginning to form and swell in the retort. This final stagecan be determined by anyone skilled in the art by observing the character of the heavy dis tillates then being collected. At this time I prefer substantially to discontinue the firing in the oven, and to close the stack ratus is accelerated so as to limit the steam pressure in the retort to a substantially small amount. .lt pointed out that when the coke is actually forming and there is nothing in the retort but substantially dry material the intensity of the heat retained by the brick-work is sufficient to complete the distillation, especially in view of the fact that with an excess of steam the hydrocarbon materials are vaporized at a much lower temperature than without the steam.

In my practice with the refined coal tar i mentioned the complete distillation to coke complete distillation, the action of the mo ordinarily consumes from eighteen to twenty hours from the time distillation actually begins. The steam is first admitted after distilling for about twelve hours. A very small fractional turn of the steam valve is made every half hour or so during the next say five hours. Thereuponthe coking stage is ordinarily reached, and thereupon the amount of steam admitted is greatly increased, which, in my practice is substantially all that can flow through a one inch pipe valve at say one hundred pounds pressure. It is at this time also that the firing is reduced and the stack damper is closed, and the distillation then proceeds to its completion, which ordinarily consumes say three more hours. The actual time consumed depends upon such considerations as the character of the tar, the intensity of the fire from the oven, the amount of steam and vacuum employed, etc., all as will readily be appreciated and put into practice by those skilled in the art.

The actual time consumed for each stage can be accurately determined by the specific gravities of the distillates from time to time. i

Assuming the method to have continued as above outlined for say twenty hours, or to uum-producing apparatus is here discontinued, but the admission of steam is continued in full force for a period of from one to six hours thereafter for the purposes of removing all obnoxious gases, cooling down the mass as a whole, moistening the mass, overcoming the tendency of the coke to stick to the walls of the retort, and the removal and dilution of combustible gases to prevent explosion and fires taking place when air is first admitted. The duration of this last mentioned period of from one to six hours is determined by the temperature in the retort, which may be indicated by a pyrometer with which the retort is equipped, but which is not shown in the drawings. Briefly stated, this period will continue until the retort is at a temperature suflicient to warrant the beginning of the cleaning-out operation, say 4E5O 'F. At this time the steam is turned entirely off.

The manhole doors 38, 39 and 58 may now be opened and a draft may be induced, by any approved means, through the top manhole openings to free the retort of the vapors of steam. At this time the temperature of the mass of coke is still greater than the boillng point of water, which causes it to dry out quite rapidly, and before the interior of the retort is cool enough to admit a workman withcomfort the coke is entirely dry. In this connection it is pointed out that the coke will be cooled progressively by the air entering the rear manhole as the workman proceeds with the cleaning out operations. After the workman has gained entrance to the interior he is supplied with a draft of air through the rear manhole.

An analysis of an average sample of coke made from the above mentioned refined coal tar in the still illustrated and in accordance ivith the method herein described is as folows:

Moisture .3770; volatile matter 4.78%; fixed'carbon 94:. l2%; ash .4370; B. T. U 15730; sulfur .770 water soluble 1.43%.

The dist'illates which are obtained are almost entirely if not entirely the result of fractional distillation, and are therefore of distinctive character, and substantially the maximum yield of these high-boiling products is obtained.

The high-boiling, high specific gravity distillates are peculiar and distinctive in appearance. They also contain a relatively low percentage of compounds which crystallize, solidify, orsettle out at ordinary temperatures. They are furthermore of such distinctive character as to render their subsequent refinement more easy, rapid and satisfactory than in the case of the highboiling, high specific gravity distillates obtainedby methods heretofore known. Owing to their distinctive character, also, it is possibleto collect them separately or to segregate them with substantial accuracy, a feature of great advantage in view of the tie sirability of subjecting certain of them to subsequent treatment.

It is obvious'that both the process and apparatusherein described and illustrated may also be employed in distilling pitch of various degrees of consistency. In distilling coal tar 'pitchof the; heavier consistencies, for instance, such as of paving pitch, the

. fines 11 and 12 located as shown in the drawstance from that point in the process of complete distillation set forth where a pitch of corresponding consistency is formed.

I claim:

1. The step in the method for the complete distillation of liquid hydrocarbon material to substantially dry coke, which is the admission of steam within the body of the mass immediately prior to, at and after the change from the substantially plastic state of the mass into the coke state.

2. The method of distilling liquid hydrocarbon material to substantially dry coke which includes heating the mass substantially uniformly throughout and agitating the mass by currents of live steam from a time prior to the formation of cokeuntil the formation of the coke.

3. The method of distilling liquid hydrocarbon material to substantially dry coke in a substantially closed retort which includes creating a partial vacuum in the retort, heating the mass, and introducing steam thereto in gradually increasing quantities as the mass increases in specific gravity, and introducing a relatively large amount of steam into the mass at about the time the coke is forming.

4. The method of distilling liquid hydrocarbon pitch in a substantially closed re tort which includes heating the pitch in the retort, creating a partial vacuum therein during the preliminary stages of, distillation, introducing steam into the mass in relatively small quantities during the latter stages of distillation, introducing materially large quantities of steam at about the final stage of distillation, and continuing the introduction of materially large quantities of steam during the complete formation of the coke.

5. The method of distilling hydrocarbon pitch to substantially dry coke which includes the fractional distillation of the volatile elements of the pitch in a still having a heating oven and a retort having masonry walls encompassing a portion thereof, the introduction of, steam to the'mass during the coking operation, continuing the coking operation by means of the latent heat contained in the structure of the still, and providing a flow of steam through the mass and out of the retort until the retort and mass are substantially cooled.

6. The method ofobtaining a high percentage of high-boiling, high specific gravity distillates from the complete distillation of hydrocarbon pitch in a substantially closed retort which includes the admission of steam within the body of the mass prior to, at and after the change from the substantially plastic state of the mass into the coke state while maintaining the top portion of the retort at a temperature at which the vapors of distillation will not decompose by contact therewith.

7. The method of obtaining a high per centage of high-boiling, high specific gravity distillates by distilling hydrocarbon pitch to coke which includes heating the pitchy mass substantially uniformly throughout by internal and external firing in a substantially closed retort, and agitating themass by currents of steam from a time prior to the formation of coke until the formation of the coke.

8. The method of obtaining a high percentage of high-boiling, high specific gravity distillates by distilling hydrocarbon pitch 'to coke which includes heating the pitchy mass substantially uniformly throughout by internal and external firing .in a substantially closed retort, agitating the mass by currents of steam from a time prior to the formation of coke until the formation of the coke, and all the while maintaining the upper portion of the retort at a temperature not higher than that at which the distillates would decompose.

9. The method of obtaining a high percentage of high-boiling, high specific gravity distillates by the complete distillation of coal tar pitch in a substantially closed retort which includes the heating of the pitch in the retort, the creation of a partial vacuum therein during the preliminary stages of distillation, the introduction of live steam in relatively small quantities during the latter stages of distillation, the introduction of materially large quantities of steam at about the final stage of distillation,-continuing the introduction of steam during the complete formation of thecoke, while maintaining the upper portions of the retort at a temperature at which the distillates will not decompose during substan\- tially all of the period of distillation.

EDWARD E. PERSHALL.

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