US2005675A - Process for cracking hydrocarbon oils - Google Patents

Description

F.' W. HALL El AL PROCESS FOR CRACKING HYDROCARBON OILS June 18, 1935.

Filed April 27. 1931 2 Sheets-Sheet 1 INVENTOR S June 18, 1935. F.'W. HALL ET AL PROCESS FOR CRACKING HYDROCARBON OILS Filed April 2'7, 1931 2 Sheets-Sheet 2 INVENTORS J if Patented June 18, 1935 Frank W. Halland Harris A. Smith-Port Tex., assignors to The Texas Company,

Arthur, New

York, N. Y., a corporation of Delaware Application April 27, 1931, Serial No. 533,042

3 Claims.

This invention relates to an improved process and apparatus for the conversion oflhydrocarbon oil to produce gasoline or motor fuel and more particularly to a process wherein the oil is-com 5 mingled with hot vapors .previously subjected to cracking and the resulting mixture of :cracked vapors and vaporized charge is fractionated to produce a desirable gasoline fraction and a heavier liquid fractioncomposed of partially-converted oil and fresh oil for cracking in the vapor phase.

In its broadest aspect the invention Comprises a-process of converting hydrocarbon oils to produce gasoline wherein a clean stock composed of a mixture of partially converted oil and fresh oil which is free from residual and potential coke forming material is continuously evolvedand conducted in the form of vapor thru regenerative heating means wherein it undergoes cracking in the vapor phase. a l

The invention also contemplates an improved combination of apparatus which is particularly well adapted for carrying out the method of the invention.

Our invention contemplates aprocess fortreating hydrocarbon oil for the production of gasoline wherein the oil which is to be cracked is heated to a vaporizing temperature and the resulting vapors are ipassed .in succession thru a series of regeneratively heatedconverters-wherein the vapors are brought into contact withhot refractory material arranged .in the form of fines or checkerwork within the convertersand adapted to heat the vapors to a conversion temperature and maintain them" under cracking conditions during their continued passage thru the-successi-ve converters. The cracked, vaporsleaving the converters commingle with fresh incomingcharge to subject the vapors to partial condensation and effectdistillation of the chargeoilso as to produce a combined vapor free from residual ortarry matter and which is subjected tofractionation to form a gasoline vapor fraction and a heavier .liquid or reflux condensate consisting of fresh oil .and partially converted oil which, .due to its freedom from heavy residual fractions, is adapted to form a clean circulating stock suitable forcirculating in a vaporous'c-ondition thru the converters and to undergo cracking therein without the production of substantial quantitiesof coke.

For our regenerative heating means we prefer to employ a plurality of converters somewhat similar to the regenerative heating stovesiused in carburetting watergas or-to the .typeusually employed in connection with blast. furnaces in steel mills. Thus, for example, when employingfour converters, the converters are preferably interconnected in such a manner as to permit flowing vapors thru three of them in succession while the fourth is being heated up by blasting or firing until the refractory material has reached a temperature of 1409" F. or higher, following which the heated converter is out i nto the system and the coolest converter cut out for reheating. Preferably the vapors are introduced to the coolest converter still remaining in operation and are finally discharged from the hottest or most recently heated converter.

When a cooled converter has been out out of the series for heating,

fuel gas may be admitted thereto to displace all the rich cracked hydrocarbon vapors remaining within the converter into suitable receiving means after which combustion is initiated in the bottom of the converter and continue therein until such time as the refractory mater desired temperature.

It has been customary in cracking hydrocarbon oils in ial has reached the the prior art when the vapor phase'to conduct the vaporized oil thru continuous tubular heating coils wherein the vaporized oil may *be subjected to relatively around 1200 F. for example. in tubes or coils in this way high temperatures, Heating the vapors has been attended with considerable difiiculty particularly that of overheating of the tubes or pipes which must be exposed to relatively high furnace temperatures in order to heat the vapors flowing thru the tubes to the desired temperatures.

Since the rate at which heat may be transferred from the walls of the tubes or pipes to the vaporous material flowing therethru is relatively'low, the tube walls are therefore subject to relatively severe heating which results in rapid deterioration of the metal and consequently shortens the life of the tube or pipe in service. is the readiness with which A further difficulty carbon is deposited on the interior surfaces of the tubes particularly when the material 'flowing thru the tubes is not 'in-a completely vaporized state and therefore in-- "cludes particles of liquid which'when precipitated-against the highly heated metallic surfaces are largely decomposed to form coke which adheres to the surface of the'metal and tends to I build up and form such a deposit that the tendency towards the overheating of the tubes is very greatly increased. For this reason it has been extremely essential heretofore in this type of cracking operation to employ only relatively light charging stocks such as kerosene and relatively low'boilinggas oils. a

In our invention where-thevaporized oil is subjected to conversion in a series of regenerative heating stoves or converters containing fines or checkerwork formed from an inert or refractory heat retaining material the Vapors may be subjected to cracking temperatures for a prolonged period of time'without subjecting'the equipment to appreciable deterioration from severe and extended heating. Such carbon as may be formed during the conversion deposits uponthe surfaces of the refractory material and when the stoves. are successively cut out of service for reheatingthe deposited carbon is "readily and advantageously removed by combustion during the reheating step during which the heat retaining mate:

Y rial during the, relatively short period of time that each converter remains on the line between reheatings, and this carbon deposit is readily removed by combustion during the reheating step so thatno operating delay is necessary to remove the carbon, and which is to be contrasted with the cracking of hydrocarbon vapors in a pipe coil heater where it is necessary to shut down at quite frequent intervals in order to manually remove the coke which has become deposited within the pipes or tubes. p

A further feature of our invention comprises continuously forming a clean circulating stock free from tarry or residual pitchy matter which might otherwise be readily decomposed to form substantial quantities of coke during passage of the oil thru the conversion zone. 3

These and'other objects and advantages of the inventionwill be better understood from'the following description considered in connection with the figures of the accompanying drawings which illustrate diagrammatically a preferred form of apparatus for practicing the process of the invention. 7 V

In the drawings, Figure 1 is a diagrammatic elevational View illustrating apparatus adapted tothe carrying out of the process of the 'invention.

Figure 2 is a diagrammatic view in plan illustrating a method of interconnecting the converters, V I

Referring to Figure 1, a pump 1 draws 011 from a source (not shown) and pumps the oil thru a line Lhaving a valve 3, leading to a reflux coil 4 located in the upper portion of a fractionating column 5 and adapted to supply cooling thereto. A by-pass 1, having avalve 3,is provided thru which oil not required to go thru the reflux cooling coil maybe passed directly into a pipe 6 leading from the outlet of the reflux coil 4 to a heat exchanger 9 thru which latter the 011 flows in indirect heat relationship with a stream of residual oil being withdrawn from the system.

A by-pass pipe I 0 is also provided to permit bypassing the exchanger 9. From the exchanger}! the heated oil flows thru a pipe H leading to the upper portion of a stripping tower I2 into the interior of which it is introduced thru a spray 13 adapted to distribute the oil over suitable packing material M such as rocks, raschig rings, bubble trays,tiles and the like.

Hydrocarbon vapors which have previously undergone cracking as will presently be described which is withdrawn thru pipe 38 leading to the first of are introduced to a lower portion oi the stripping tower I2 thru a transfer line l5, after flowing either totally or in part thru acoil l6 located in the bottom of the strippingtower and adapted to supply heat for reboiling the liquid collecting in the bottom of the tower. The cracked vapors in passing upwardly thru thev packing material l4 come into intimate and direct contact with the downwardly flowing charge oil thereby cool- 7 ing and partially condensing the vapors and vaporizing the bulk of the charge oil. The liquid collecting'in the bottom of the stripping tower l2 which is composed of the unvaporized residual portions of the charge and tarry material condensed out of the cracked vapors is withdrawn thru a pipev l1, having a valve l8, to the heat eX changer 9 in which it is cooled while imparting its sensible heat to the incoming charge. A portion of. the liquid being withdrawn thru the pipe I! may be conducted thru a pipe I9, having a valve 20, leading. to a coil 2| placed in the bottom of the fractionator reboiling the liquid condensate collecting in the bottom of the fractionator and thereby facilitate fractionation within the tower. The oil leaving the coil 2| is preferably returned thru a pipe 22 to the heat exchanger 9 from which it may be withdrawn and disposed of as may be desired.

The vapor mixture rising to the top ofthe stripping tower I 2 is conducted thru a pipe 23 to the middle portion of the fractionator 5 wherein it is subjected to fractionation to form avapor fraction, consisting of gasoline and fixed gases, and a relatively higher boiling liquid fraction collecting as a reflux condensate in the bot- I. tom of the fractionator.

The gasoline vapor is withdrawn from the top of. the fractionator 5 thru a pipe 24 leading to a condenser 25 wherein it is cooled and condensed to form a distillate accumulator or receiving drum 21 wherein the non-condensable fixed or dry gases are separated from the gasoline liquid to be withdrawn thru a pipe 28 while the gasoline liquid may be withdrawn thru a pipe 29 to storage or for further treatment.

The surplus reflux condensate collecting'in the bottom of thefractionator 5 and which is composed of the fresh gas oil portion of the charge in admixture with clean circulating stock for vapor phase cracking, is withdrawn thru a. pipe 30 and conducted 'by means of a pump 3| thru a line 32 leading to a pipe coil 33, in a suitable furnace 34, and wherein 1- 'the stock is heated to a vaporizing temperature,

preferably under superatmospheric pressure.

The heated-oil is discharged from the' heating .coil' thru a pipe 35, having a'valve .36,*into a vaporizing chamber 31 preferably'maintained at a pressure lower than that maintained in the neating coil. Upon introduction to the vaporizer the heated material is substantially entirely a series of concollecting in the thru a pipe 40,

porized oil is admixed'with incoming charge and;

returned to'the system for further treatment.

If desired, this unvaporized oil maybe conducted thru a pipe 44, having a valve 45, leading to an atomizer or jet nozzle 46 interposed in the 5 adapted to supply heat fora pipe 26 leadingto an the partially converted oil ,manifold 69 thru the pipe 6|.

aor ztcv-s vapor line 38. 1 The velocity of the vapors flowing thru the atomizer 45 may be sufliciently high to'entrain the'liquid, which is usually relatively small in amount, and convert it to a mist of finely dividedform.,

The vaporized oil enters the lower portion or combustion chamber 41 of the first converter and flows upwardlythrua flue 48 to the top of the converter from which point the vapors pass downwardly thru highly heated checkerwork material 49 and as a result of intimate contact with this refractory material the vaporsare heated to a suitable cracking temperature. From the bottom of the checkerwork the vapors are passed thru a pipe 52 to the inlet of the next succeeding converter; From the bottom of the last converter the cracked vapors are passed into the transfer line I5, already mentioned, and which leads to a mid point ofthe stripping tower l2.

Referring to Figure 2, the vaporized oil flowing thru the pipe 38 is conducted to a manifold 60 with branch pipes 61, 62, 63 and 54, each having a .valve65, leading to the pipes 5|; 52, 53 and 54, each having a valve 55, interconnecting the four converters 390 39b, etc. Vapor discharge lines 56, 51,-58 and 69, each having avalve HI, connecting with the pipes 5!, 52, etc. form. vapor outlets for each converter leading to a main vapor line H from which the vapor stream is conducted thru the transfer pipe !5 to the stripping-tower as. already described. Purging out pipes I2, 13, 14 and 15, each having a valve 15, are provided thru which vapor remaining in any stove aftervit has been cut out of the system for reheating maybe displaced to a suitable gasometer Tl in which the heavier portions of the vapor may condense and be withdrawn therefrom thru a pipe 18 for subsequent return to the system. The uncondensed gaseous material remaining in the gasometer is available as fuel gas for combustion purposes during the reheating operation and which gas is'conducted thru a pipe 19 leading to fuel gas inlets or burners 85 provided with air inlets 8|, and extending into the combustion chambers 41 of each of the converters. When operating with four converters as illustrated in the diagram. and where the vapors are flowing thru three of the converters in succession while thefourth is being reheated, the vapors may, for v example, enter the combustion chamber 41 of the coolest converter 39a from the After passing downward thruv the checkerwork in this converter the vapors pass thru the connectingpipe 52. to the combustion chamber of the next succeeding and hotter converter 39b and from which, after passing therethru, they flow thru the pipe 53 to the third and hottest converter 39c from which the cracked vapors are then passed thru the pipe 58, leading from the pipe 54, and are conducted into the main vapor line H leading to the transferline l5. .The converter39cl may be segregated or isolated from the series in order to "undergo reheating by closing the valves 65 and 55 in the pipes 64 and 54, respectively, and" also closing the valves 55 and Hi inthe pipes 5| and 69, respectively. At the time of segregating it from the rest'of the converters it will, of course, be filled with partially converted vaporized material and uponcutting it out of the system'these rich hydrocarbon'vapors may be displaced from the converter by introducing fuel gas, or preferably the fixed'or dry gases which havebeengenerated der pressure from the pipe 28 leading from the accumulatordrum 2'5, thru the pipe'lfl and the burner 80 to the combustion chamber of the converter. checkerwork displace the richer hydrocarbon va pors thru the pipe. leading to the gasometer As soon as these rich vapors have been substantially completely displaced from the converter the necessary amount of air may thenbe introduced thru the burner extending into the combustion space of the converter and combustion of the entering dry gas. initiated. The supply of air may be regulated so as to substantially confine the flame to the combustion chamber and from which the hot products of combustion pass, upwardly thru the interior flue 43 and then pass downwardly thru and over the checkerwork to heat it up, the period of combustion being prolonged for a sufficient time, preferably for not over an hour, to heat up the refractory material to the desired temperature which will usually range from aboutl300 to 1400? F; The hot flue gas leaving the converter during the reheating step may be discharged into a flue 82 leading to a stack 83'thru which it may be discharged to the atmosphere, although advantage may be taken of its sensible heat content by returning a portion of the hot flue gas by meansof a fan 84 thru a :pipe 85 to the furnace 34.

When the refractory material has attained the desired temperature the flow of air to the burner 80 may be topped thus extinguishing the flame and terminating combustionv whereupon the valve 55 in the pipe 54 and the valve 55 in the pipe 54 may be opened and also the valve 10 in the pipe 58 closed allowing the hot vapors from the converter 390 to enter the newly heatedcone The fixed gases in flowing thru the 1 1n the process and which may be withdrawn un- I verter 39d and pass therethru into the pipe 69 tem and reheated in a manner similar to that.

just described;

In the practice of our invention a charge stock,

which may comprise crude oil, after being pre- 7 heated during passage thru the reflux coil 4 and the heat exchangerv 9, is introduced to the stripping tower l2 wherein it is commingled with a stream of vapors previously subjected to cracking in order to condense undesirable tarry constituents out of the vapors as well as to effect distillation of the substantial bulk of the crude. The tarry matter condensed out of the cracked vapors together with'the residual portion of the crude collecting in the bottom of the stripping tower I2 may be withdrawn from the system as a fuel oilor to be used in any other desirable manner. i

The resulting vapor mixture comprising the partially cooled cracked vapors and the natural gasoline and gas oil fractions of the crude charge is introduced thru the pipe 23 to the fractionator 5 wherein it is subjected to fractionation to form a'vapor fraction-composed of the natural gasoline constituents of the charge and those fracto the accumulator drum 2! wherein the fixed gases are separated from the gasoline. distillate. That portion'of the crude charge-exclusive of its natural gasoline constituents and comprising fresh gas oil which is condensed in the fractionator 5 together with the relatively high boiling and partially converted portions of the cracked vapors, is withdrawn thru the pipe 30 and pumped thru the pipe 32 to the heating coil '33 wherein it is heated to temperatures of around 700 F. or higher and preferably under pressureswhich may range from somewhat above atmospheric to 400 or 500 pounds or even higher. The heated oil is expanded thru .the valve 36 into the vaporizing chamber 31 which may be maintained at a pressure substantially lower than that within the heating coil in order to facilitate substantially entirelycomplete vaporization of the heated oil. It is" contemplated that the conditions of temperature and pressure may be'regulated to whatever extent is necessary in order to effect substantially complete vaporization upon introduction to the vaporizing chamber.

It is desirable to introduce the hydrocarbon oil to the converters in a completely vaporized condition since when substantial amounts of :liquid in the form of droplets or particles are introduced to theconversion zone wherein the particles come into contact with the refractory material a rapid decomposition of .the liquid particles may take place with the production of substantial amounts of coke. The decomposition of liquid into coke under these conditions is believed to take place to a materially greater extent than is the case with oil which is, entirely in the form of vapor or as a fine mist.

While the vaporizing oil mayin many cases be introduced directly from the coil outlet to the first converter which is under sufficiently lower pressure than the heating coil to result in sufliciently complete vaporization of the oil upon its introduction to the converter, means have been provided to facilitate separation of liquidparticles from the vapor prior to its entry tothe conversion zone. This unvaporized material may be Withdrawn from the bottom of the vaporizing chamber and be either admixed with the fresh charge entering the system or passed --thru the atomizing means 46 wherein advantage may be taken of the atomizing effect of vapors flowing thru the atomizer at a high velocity to convert this liquid, which under ordinary conditions, is of relatively small amount, to a sufficiently fine state of division such that its introduction to the converters is not attended with a substantial amount of decomposition to form coke or carbon.

The vaporized oil may enter the first converter of the seriesat a temperature of from 700 to 800 F. and in passing thru the heated checkerwork of this converter may be heated tofrom 900 to 1000 F. From this converter it' fiows'thru the second or intermediate and next hottest: converter of the series wherein the vapors may'be heated to from l000 to ll00 F.' while in the third andhottest converter they may be raised to a temperature of from 1100 to 1300 F. The degree and frequency of reheating of'the converters may be regulated so that the temperature of the vapors finally leaving the conversion zone may be consistently around 1200? a F., although higher temperatures may readily be maintained merely 2,005,670 I converters: arranged in series thetemperature of the vapor leaving the last converter may be maintained substantially uniform withoutmaterial .the vapors are subjected to a substantial period of digestion at high temperatures when fiowin'g thru the series of three or more converters in succession, which extended timeof digestion is desirable from the standpoint of extending the degree of the conversion reaction, that is, to increase the amount of cracking with the consequent production of larger yields of gasoline or It is contemplated that'any desired pressure may beemployed and that a uniform pressure may be maintained throughout the entire system, although ordinarily it may prove more desirable to maintainthe heating coil or pipestill under superatmospheric pressure,'releasing the pressure somewhat in thevaporizing chamber, maintaining a, reduced superatmosphericpressure in the converters,,and reducing the pressure still further, or to approximately atmospheric pressure in the dephlegmating means;

, Obviously many modifications'and variations of the invention, as hereinbefore set forth, may be made without departing from'the spirit and scope thereof, and therefore, only suchnlimitations should be imposed as areindicated in the appended claims. 7 V '7 We'claim: t

1. The process of treating hydrocarbon oil which comprises passing a clean relatively heavy oil through a heating zone wherein it is raised to a vaporizing.temperatura'separating the resulting heated oil into'vapors and a liquid residue, passing saidfvapors, through a converter zone in contact with highly preheated solid re fractory material wherein said vapors are raised to a cracking temperature controlled independently of said vaporizing temperature and are subjected to'conversion by the contained heat of said preheated refractory material, removing resulting cracked products and introducing them into a separating zone wherein vapors separate from liquid residue, removing vapors from the separating zone and passing them directly into a fractionating zone independent of said heat variations therein due to periodically cuttingout one converter for reheating and cutting into-the series a newly reheated converter." Furthermore,

andv passing it through said heating zone as said clean oil first mentioned and introducing fresh relatively heavy charging stock into said separating zone in contact with the introduced cracked products to cause at least'partial'vapon ization of said charging stock, and removing liq- I uid residue from said separatingzone.

2. A process in accordance with claim l wherein liquid residue left after separating vapors from the heated clean oil removed from the heating zone, is introduced into said separating zone in contact with the hot cracked products intro- 5 duced thereinto from the converter zone.

3. A process in accordance with claim 1 wherein liquid residue left after the separation of.

vapors from the heated clean oil removed from the heating zone is introduced in mist form into said converter zone.

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