US1761340A - Art of cracking hydrocarbons - Google Patents

Description

June 3, 1930. .E. c. HERTHEL 1,761,340

ART OF CRACKING HYDROCARBONS Filed Oct. 27, 1927 ATTORN EYS 'il atented dnxiefi, 193d UNITED STATES EUGENE o. nnn'rnnn, or CHICAGO; rn'nmors, nssrsnon 'ro siNcLAIrt nnrnime comr sex or New YORK, n. Y.,

PATENT: OFFICE,

A conrorm'rrou or MAINE Am or cnncxme rrxnaooaanous Application filed October-27,1927. Serial No. 229,099.

This invention relates to improvements in the cracking of high-boiling and easily .cracked hydrocarbon oils, such as heavy'gas oil and pressed wax distillate, for the'produc tion of gasoline. In order to maintain a high rate of production from a given installation,

it is usually desirable to carry out such crack ingoperations forthe production of gasoline at relatively high cracking temperatures.

The heavier and higher boiling hydrocarbon oils, such as those just mentioned, tend ;to decompose with the formation of excessive quantities of, gas and carbon or heavy pitch at cracking temperatures, and this tendency is more pronouncedas the cracking temperature increases. In pressure distillation processes in particular, this tendency involves several objectionable incidents which increase the difliculty of cracking such stocks and which make such stocks less desirable as raw material for the production of gasoline. This invention relates particularly to improve- 'ments in the cracking of such high-boiling and easily cracked hydrocarbon oils by dis tillation underpressure and provides an improved method of operation in which difiiculties, such as those just mentioned, are

avoided or minimized.

According to the present invention, the, high-boiling easily cracked stock is subjected to the cracking conditions of temperature and pressure maintained in the cracking opera-- tion in admixture with a low-boiling refractory stock, and the mixture is proportioned so that sufiicient heati'is absorbed in vaporization of the low-boiling refractory stock to avoid objectionable over-cracking, with excessive formation of gas orcarbon or heavy pitch, of the high-boiling easily cracked stock. A maximum proportion of the heat so absorbed in vaporization of the low-boiling refractory stockisin turn absorbed in fresh :"P

stock supplied.tothe-operation so that this heat is not permitted to escape. This last mentioned heat recovery is advantageously carried out by direct heat exchange between .the fresh stock and the vapors from the cracking operation with condensation and return in admixture withthe fresh stock of a maximum proportion" ofthevaporized low-boiling refractory stock. In addition to the. fresh high-boiling easily cracked stock, additional -low-boiling refractory stock is supplied as the operation proceedsto maintainoptimum conditions, particularly with respectto over-' cracking of the high-boiling easily cracked stock.

In carrying outthe invention, thus, a lowboiling refractory stock' is maintained in cyclic circulation-through aheating zone, a

vaporizing zone and a refluxing operation and the volume of this -low boi1ing refractory stock in such circulation is maintained by the supply of additional low-boiling re fractory stock'during the operation as this stock escapes as part ofthe distillate product. Under some conditions, this low-boilin refractory stock may in part be cracked an to this extent escape as part of the cracked product. Hydrocarbon oils not less than 9.0% of which boil ofl up to 550 F. are articularly advantageous low-boilingqre rac-- tory stocks for use in carrying out this in- Avention. To eliminate or reduce further vaporization of the low-boiling refractory stock tion, the vaporizing zone and refluxing oporation are maintained under superatmospherrc pressure, advantageously under a pressure approximately the same as that at which the hot oil products are discharged from the heating zone. The high-boiling easily cracked stock to be cracked is introduced into direct contact with vapors in the refluxing operation. nents of the vapors including a maximum proportion of the low-boiling refractory stock isthus condensed at the same time that the fresh stock is preheated by this heat exchange. The resultingioil mixture including the reflux condensate and the unvaporized fresh stock is then' circulated to the heating zone. The heat absorbed in the heating zone in vaporization of the low-boiling refractory stock to protect the high-boiling easily cracked stock against over-cracking is thus returned, at least in large part, to the crack ing voperation proper. In the heating zone, the oil mixture is heated to a suitable cracking temperature under a suitable pressure,

The heavier compov say to 725 77 5 F. under a pressure in. the

neighborhood of 80120 pounds per square inch, to effect the desired cracking. The pressure in the heating zone should not exceed a value beyond which vaporization of the low-boiling refractory stock in the heatfing zone at the prevailing temperature in the heating zone is insufiicient to have the desired protective efiect in avoiding overscracking of the high-boiling easily cracked stock. From the'heating zone the'hot oil products are discharged into the vaporizing zone and from the vaporizing-zone the resulting vapors escape to the refluxing operation and unvaporized oil isdischarged in the usual way. The vapors uncondensed in the re- .fluxing operation are taken off and condensed to form a distillate product including the cracked gasoline product and a part of the low-boiling refractory stock. The high.-

boiling easily cracked stock to the treatment of which the invention particularly relates are those hydrocarbon oils not more than 50% of which boil off up to 600 F; During 'for example.

the operation, the low-boiling refractory stock is supplied at an average rate maintained in excess of 5% of the total rate at ,which fresh stock is supplied and the highboiling easily cracked stock is supplied-at,

the average rate maintained in excess of 50% of the total rate at which fresh stock is supplied, excluding that amount of oil required initially to charge the still system. Thus with a total rate of feed of 1200 gallons per hour, the rate of'supply bf low boiling oil would be supplied at a rate in excess of about 60 gallons per hour while the high boiling oils would .be supplied at a rate in excess of about 600 gallons per hour, In general, the more easily cracked the high-boiling stock, the larger, is the percentage of the low-boiling refrac tory stock fed to the still. The cracking conditions maintained in the operation may also be reduced in severity with more easily cracked stocks, but in general it is advanta; geous to increase the proportion of low-boiling refractory stock supplied to the operation at least up to the point where heat lossbecomes excessive. H

.One form of apparatus adapted for carryillustrated in Letters Patent No. 1,285,200

issued to the Sinclair Refining Company, November 19, 1918 on the application of Edward W. Isom.

The pressure still illustrated comprises the bulk supply drum 1, a bank of heating tubes 2, arranged in the heating flue of a furnace 3,

and circulating connections 4. 5 and 6; in-

.the condenser or receiver.

escapefrom the bulk supply drum through vapor line 9,'into the lower end of the reflux tower. Vapors remaining uncondensed escape from the upper end of the reflux tower through vapor line 10 to the condenser 11..

This condenser is arranged to discharge into the receiver 12 from which the distillate product is discharged throughconnection 13 and uncondensed vapors and gases through connection 14. The pressure in the system may be'maintained and regulated by means of valve 15 arranged in the vapor line between the reflux tower 8 and the condenser 11, or by means of suitable valves arranged beyond Connection 16 is provided for theintroduction of fresh stock into the upper end of the reflux tower 8. The oil mixture collecting in the lower end of thereflux tower 8 may be supplied to the circulating still charge through connection 17 or mav be forced into the circulating still chargev t rough connections 18, 19 and 20 by means of pump 21. -Additional fresh stock may be supplied to the circulating still charge through connections 22 and 20 .by means of pump 23. Connection 24 is provided for discharging pitch-laden oil-or tar from the bulksupply drum 1 during operation. Connection 25 is provided for initially charging the still and for pumping out the still at the end of a run. Cool oil for example a part of the fresh stock is supplied through connection 26 for cooling and lubricating thebearings of the circulating pump. Part of the fresh stock may thus be supplied to the circulating still charge through the pump bearings. The exposed parts of the still system including the reflux tower 8, the bulk supply drum 1', the circulating connections tem of the type illustrated, the still is initially charged with say about 8,000 gallons of gas oil and brought to cracking conditions of temperature and pressure in the usual way. If the stock to be cracked has a particularly marked tendency toward over-cracking, the initial still charge, instead of being made up of this stock, may consist of some more refractory stock, say an ordinary gas oil. After the still is brought to operating conditions of temperature and pressure, vapors are taken off through the reflux tower to the final condenser and the introduction of fresh oil through connection 16 is begun. The refluxing operation carried out in tower 8 for example, may with advantage be controlled by regulating the rate at which fresh stock is supplied through connection 16. About the 24: is begun. As reflux condensate together with unvaporized fresh stock accumulates in the lower end of the reflux tower it is returned to the circulating still charge either through connection 17 or connections 18, 19 and 20. The latter mode of operation is particularly advantageous as it provides for positive forcing. by means of pump 21', of the oil mixture from the, reilux tower into the oil stream entering the heating tubesQ. The

low-boilingrefractory stock and the high-" boiling easily cracked stock may be supplied during theoperation either separately or ii For example. the high-boiling stock may be supplied entirely through connection 16 except for a small part supplied through connectionQG and the low-boiling stock supplied through eonnectioir22. 01', a mixture of the high-boilingtand low-boil ing stocks in appropriate proportions may be supplied through connection 16, any additiona] low-boiling stock required being supplied through connection Although the proportion of low-boiling stock in mixtures supplied through connection 16 may be increased to increase the refluxing action in the tower '8 it is usually advantageous to limit the proportion of low-boiling stock supplied through fiuxing operation, heating the oil mixture to a cracking temperature under a superatmospheric pressure low enough to permit vaporization of the low-boiling refractory stock at the maximum temperature to which the oil mixture is heated, circulating the vapors separated in the vaporizing zone to the refluxing operation, discharging unvaporized oil from the vaporizing zone, taking oit from the refluxing operation and condensing a vapor mixture including vapors of the lowboiling refractory stock and of the cracked gasoline product, and supplying a low-boiling refractory stock not less than 90% oii which boils ofi up to 550 F. to the oil mixture circulating to the heating zone, the average rate of supply of the low-boiling refractory stock not less than 90% of which boils off up to 550 F. being maintained in excess of 5% and the average rate of supply of the high-boiling easily cracked stock not more than of which boils off up to 600 E.

being maintained in excess of 50% of the total rate at which fresh stock is supplied during the operation excluding initial charge.

In testimony whereof, I have subscribed my name.

EUGENE C. HERTHEL.

connection 10, or to avoid the introduction of low-boiling stock through this connection, to reduce or eliminate any heat loss due to vaporization of such low-boiling stock in the reflux tower.

While the invention is of special value and application in connection with the operation of pressure stills of the type illustrated, it is also useful in connection with the operation of pressure stills in which unvaporized oil is not returned from the vaporizing zone to the heating zone. A suitable apparatus for carrying out this latter embodiment of the process of the invention might be illustrated, for

example, by removing the circulating con:

nection 4 in the apparatus illustrated and suitably closing the connections left open by the removal of this circulating connection.

I claim:

An improved method of cracking highboiling easily cracked hydrocarbon oils, of which not more than 50% boil ofi' up to 600 F. at atmospheric pressure, for the production of gasoline, which comprises maintaining in cyclic circulation through a heating zone, a vaporizing zone and a refluxing operation all under superatmospheric pressure

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