US2335531A - Reforming system - Google Patents

Description

Nov. 30 1943.V F. H. PRMcaEl 2,335,531

REFORMING SYSTEM l Filed March 11, 1942 MHA? 60: 47

6in1/Mfma@ ATTORNEY.

Patented Nov. 30, 1943 ,2,335,531 REFoeMING SYSTEM Frank H. Praeger, Merion, Pa., assigner to Petroleum Conversion Corporation, a corporation of Delaware Application MarchY 11, 1942, Serial No. 434,304

19 Claims.

My invention relates to oil cracking and reforming systems, more particularly to systems for increasing the antiknock characteristicsy of naphtha or straight run gasolinel and has for an object the provision of a cracking or reforming system of the true vapor phase type, in which the compressor has been entirely eliminated.

A further object of my invention is the provi- Sion of a system in which there is a substantial conversion of normally gaseous products into constituents Suitable for inclusion in motor fuel. A further object of my invention is the provision of a simple, reliable, and inexpensive reforming system in which not only the compressor hasY` been eliminated, but also in which the system as a whole, and in which the operation thereof, has been made simpler, easier, and more effective.

It has been characteristic of true vapor phase systems as previously proposed, such for example in Beardsley et al. Patent #1,842,318, Sachs Patents #2,0l6,297, #2,073,456, and Nash Patent #2,222,682 to derive from the system or elsewhere a hydrocarbon heat-carrier gas which after elevation to Suitable pressure passes through a heating coil where it is elevated to a suiciently high temperature to produce rapid cracking of a stream of vapors after mixture therewith. While systems of this character are now in operation and have proved commercially satisfactory, both the initial cost and the operating cost of the compressor used to produce the flow of gas through the system represent a .substantial investment. Nevertheless, the compresso-r has heretofore been deemed an essential part of systems of the foregoing character because it was believed necessary to provide a large quantity of circulating gas per barrel of the hydrocarbon vapors to be mixed therewith.

In carrying out my invention in one formthereof, I have found that by charging a naphtha to the reforming System as an absorbing menstruum, suiiicient gas may be absorbed Which, in addition to a stream of cycle gas withdrawn at high pressure from a stabilizing System, provides the requisite minimum quantity in the system. More particularly, by countercurrently contacting the normally gaseous constituents in the system with the charging stock, a considerable quantity thereof is absorbed. From the reformed naphtha there are removed in the stabilizer gases largely'comprising Css and Cis, or those having three to four carbon atoms per molecule and these gases form the supply of cycle gas. The stabilizer is maintained under relatively high pressure so that the derived gases may flow directly through a heating coil without needfor a compressor Since these gases, forming the 'heat-carrier, are fused to produce the reformngo'f 'the charge. "A part' of vthese gases is converted into' constituents suitable for inclusion in the iinal 'motor 'fueliproducta'xid an increase in the yieldof desired ,productis thereby obtained.`

While my 'invention is particularly adapted: to reforming operations, itis also effective in" reducing Athe size of th Compressor 'in gas oil cracking units, or in units forf crack-ing materials heavier than vgas oil.

' For a more completeunderstanding,of my invention, reference shouldfnow be had to the drawing in which I 'have diagrammatica'lly illustrated in Fig.l l a system embodying a preferred form of my invention, single .lines for'the most part indicating the connecting pipe lines; Fig. Z-ris a graph wherein I have plotted yield in volume per cent against octane numbers.

Referring to the drawing, Ihaye shown my invention in one form as applied4 to'a"reforming system in whichthe charge,'such for '.example, as heavy naphtha, enters .the system through supply line Ivi), and by pump vI.I is'elevatedtoathe pressure of the absorber l2, around 150.# per square inch gage. The charge ows downwardly over a plurality of traysA .(not shown) of the ybubble type, or other.' meansA included in the absorber I2 for providing intimate jcontact between Athe charge and gases introduced .intothe absorber by way of line I3. To .increase the quantity of gas absorbed, .an .intercooler ,L4 is preferably provided about mid-way ofthe .absorber with cooling water circulatedtherethrough as indicated at I5. Wherever .cooling `v aterf is used','inlets with a controlvalve .(not shown) and outlets are indicated by the. reference'numeral I5. Depending upon the size of the system, .the temperatures of the charge and the'coolingwater, additional intercoolers may be provided and arranged at several places along the absorber. :The lighter gases, not absorbed. are withdrawnlfrom the system byv way of line lI6 under controlof a pressure regulatingl valve I1.

The rich oil comprisingv thenaphthapcharge and the absorbed gasesarewithdrawn yfronrthe bottom of the absorber,v elevatedinpressure by the pump I8 and under the. control-pcf; the Valve I9 passthrough a heat exchangerzandzby,way of line 2| toA aheatingfcoi122 of agheaterllv which is illustrated asiof the .double',end-.,fired type. As later` explained, the .rich oil is; elevated lin temperature during. passage throughtheheat .exchanger .2D and its .temperatllrfspffurther sel known as the scrubber. gases after intimate mixture with the scrubbing =from by way of line 3|. 'per part of the scrubber section of the vessel or stream serves the creased by passage through the coil 22 of the heater 23. The absorbed gas assists in vaporizing the naphtha, the vaporization thereof being complete materially before exit from the coil 22. After complete vaporization of the charge, the vapors are further elevated in temperature until they reach a discharge temperature of approximately l3.00) to 1080 F. The time of heating is relatively short, particularly after the vapors reach an elevated temperature and the design is such that the vapors enter the transfer line 24 with little, if any, thermal cracking or reformation thereof. Concurrently with the foregoing, cycle gas by way of line 25 passes through coil 2B of the heater 23, where it is elevated in temperature to between 1200 and 1300 F. and in the transfer line 24 it comrningles with the vaporized charge.

The cycle gas serves as a heat-carrier and when commingled with the hot vapors substantially instantaneouslyl elevates' their temperature to a rapid crackin-g or reforming temperature.

The mixture of the heat-carrier gas and the vapors then enters a reaction chamber 28 so designed that sufficient time is provided, by the flow of the vapors and gas from the top of the reaction chamber to the outlet, to permit the substantial'completion of the desired reforming reaction. The vapors and gas exit through a trans.- fer line 29, connecting the reaction chamber to the lower part of a combined scrubber-fractionating column 35. In the transfer line 29, and preferably as the vapors and gas enter the scrubber-fractionator 36, they are thoroughly contacted, scrubbed and Washed by the heavy residuum withdrawn from the bottom of the scrubber 3U by Way of line 3i. This residuum, after passing through the heat exchanger 29, enters a surge tank 32, and is Withdrawn therefrom by a pump 33 and returned to the transfer line 29 by way of line 34.

The relatively hot residuum withdrawn from lthe scrubber is effective, during passage through `the heat exchanger 26, in materially elevating 'the temperature of the rich oil flowing through vthe heat exchanger 2t in heat exchange there- "with, Excess residuum produced in the system flows from the top of the surge tank 32 by way of line 35, is reduced in temperature by cooler 36, through which there is circulated cooling water, and is withdrawn to storage under the control ofvalve 38 by way of line 39.

After the thorough washing and scrubbing of the vapors and gas by the heavy oil, they rise upwardly through the scrubber-fractionator 33.

-The lower part of the vessel 33 performs the functions heretofore performed by a separate ves- IlChus the vapors and medium are introduced into a fairly large free space within the lower portion of the vessel 3i).

A'The vapors and gases rise upwardly and enter the fractionating section, While the scrubbing medium and condensate, the residuum, iiows to the bottom of the tower or vessel 3G and exits there- Preferably near the uptower there is provided a collecting deck (not shown) from which a heavy oil is withdrawn 'by way of line 4i), pump 4I, and under the con- Vtrol-of valve 42 flows through a heat exchanger 43,*a reboiler 44 and by way of line 45 is returned A'-to the tower 3B several trays above the aforesaid The withdrawal of this side collecting deck.

desirable function of removlng heat from the rising gases and vapors, and the side stream also comprises the reboiler oil or heating medium for the reboiler 44 associated with the stabilizer later to be described. The upper part or section of the vessel 30 performs all of the functions normally provided by the usual form of fractionating column or bubble tower. By suitable means, for example by a plurality of trays and bubble caps (not shown) disposed in the upper portion of the vessel, the rising vapors and gases are countercurrently fractionated by reflux pumped into the top of the column.

The overhead stream from the tower 3U comprising the gases and materials suitable for inclusion in motor fuel is withdrawn through line 41 and successively passes through a heat exchanger 48 and the main condenser or cooler 49 and thence into an accumulator 59. The normally incondensible gases of the system, those which remain uncondensed in the accumulator 5), are withdrawn from the accumulator by way of line i3 and flow directly to the absorber l2 where they are contacted with the heavy naphtha or charging stock. Condensate is withdrawn from the accumulator by way of line 5I, a part by pump 52 being returned under the control of valve 53 to the upper part of the tower 3Q as reflux therefor. The remaining part, by pump 54 under the control of valve 55, passes by Way of line 5S through exchanger 48 where it is elevated in temperature by heat exchange with the overhead products flowing therethrough. After its elevation in temperature in exchanger 48, the condensate flows by way of line 51 into the stabilizer 58. This condensate, or stabilizerfeed includes not only materials suitable for motor fuel but a substantial proportion of lighter materials such as hydrocarbons having two, three, and four carbon atoms per molecule. In the stabilizer 5S the charge is counter-currently contacted with reflux by suitable means, for eX- ample by a plurality of bubble trays (not shown). A stream from the bottom of the stabilizer is withdrawn by way of line 6i! and introduced into the reboiler 4G. It is elevated in temperature by exchange with the reboiler cil so that the lighter constituents separate therefrom and return by Way of line Eil to the stabilizer 58. remaining condensate, denuded o-f its lighter constituents, is withdrawn by way of line t2, cooled in cooler 53 and under control of valve 64 may be sent to storage as stabilized gasoline, the principal end-product of the system.

The lighter fraction of the stabilizer feed is Withdrawn as overhead from the stabilizer 58, passes by way of line 65, condenser 66 and under the control of valve 68 flows into accumulator E9. Ccndensate in the accumulator is with.- drawn by way of pump 'l0 and under the control of valve 1i is returned to the upper part of the stabilizer 53 as reflux therefor. Gases and uncondensed hydrocarbons are 'withdrawn from the top of the accumulator 59 and under the control of valve i2 ow by way of line 'i3 thrcugh the exchanger 43 and thence by way of line 25 to the coil 26 of the heater 23. The overhead from the accumulator 59 thus comprises the source of cycle gas or heat-carrying medium.

- I have found it desirable to elevate the ternperature of the cycle gas by heat exchange with the reboiler stream and for this purpose there has been provided the heat exchanger 43. There is an advantage in reducing the temperature of the reboiler medium 40 before its introduction not to be strictly limited to the exact operating conditions (temperatures and pressures) Set forth below, it is believed the unexpected results which have been achieved as a result of my invention may be more fully appreciated by the following description of a typical embodimentof my invention as applied to different charging stocks.

For example, a relatively heavy naphtha, one having a gravity of 53.2 A. P. I., an initial boiling point of 211 F., a 50% point of 289 F., a 90% point of 377 F., and an end point of 418 F. was charged to the absorber by the vpump II, the pump having a discharge pressure adequate to insure induction of the naphtha into the vabsorber, operating at from 150 to 160 lbs. per square inch gauge. This pressure is maintained by the valve I'I as before explained. At the same time, lighter gases from accumulator I] flow `into the absorber I2 by way of line I3 due to the 'fact the tower 30 and the accumulator 50 operate at higher pressures, For example, the pressure on the accumulator 5U is maintained at from 155 to 170 lbs. per square inch gauge. These gases consist largely of hydrocarbons having from one to three carbon atoms vper molecule, although a small percentage of C4 and heavier compounds may be present. In the described operation, there were present not more than about7 to 10% by weight of C4s and C5s and higher.

During its countercurrent contact with the charging stock, about 40% to 50% of the total number of cubic feet of gas entering theabsorber I2 was absorbed. This corresponds with an absorption of the gases by'between 52% to 59%, by weight. With this degree of absorption and without excessive cooling of the charging stock, the rich naphtha, now about 130 vol. per cent of the llean naphtha, was charged to coil 22. The vapors and gases in the heating coil were elevated in temperature to between 1050 and 1135 F. and discharged into the transfer line 24. The stabilizer 58 andthe accumulator 69 operate at pressures from 250 to 275 lbs. Thus the gasesrich in C3s and C4s readily flow from the accumulator 69 through the exchanger 43 and by way of line to the coil 26 of heater 23. The heat carrier or cycle gas consists of Css and C4s to the yextent of about 60g-70%, the remainder thereof being made up of both heavier and lighter hydrocarbon gases. After elevation of the cycle gas to about 1200 F., it commingles with the heated vapors and gases from coil 22 quickly to elevate their temperature and to initiate reforming thereof. A reaction time for the mixture of hydrocarbons of the order of one to two minutes was provided by the reaction chamber 28,

The scrubbing oil, in quantity from one to two Vtimes that of the charging stock, consisted of a v.has been necessary to utilize a compressor to .elevate the gases .from the .accumulator 50 to a `sufficiently high vpressure for introduction into the flash gas coil 22, or into a flash drum. In

accord with my invention, the gas flows from accumulator '50 to the absorber I2 and afterthe absorption `of the gases by the charging stock the enriched naphtha is readily introduced into vthe coil 22 at a pressure adequate to insure vthe maintenance on the scrubber-fractionator and accumulator 50 of a pressure to insure the return .flow of the gases to the absorber I2 by way o'f line I3. In other Words, by absorbing the gases in the'liquid charge, the enriched naphtha vmay be elevated as a liquid to any desired pressure and there is avoided the need for a compressor separately to elevate the pressure of the gases for introduction into the coi122.

As indicated on the drawing, there may be vintroduced into the line 55 by way of line'15a'light naphtha, itself not suitable as motor fuel, but which can 'be blended with the reformed heavy naphtha to produce a greater yield of stabilized gasoline. In the embodiment of my 'invention now being described, this light naphtha, having an end point of about 200 F., represented about 30% by volume of the lean or heavy naphtha introduced through line I0. About 34% of this light naphtha consisted of compounds having ve carbon atoms per molecule and less.

In accord with the rforegoing embodiment of my invention, there was produced a yield of 83.7% by volume of stabilized gasoline having an octane number 39 research method, of 77.2. By the Aaddition of only 1 cc. of tetraethyl lead this octane number was increased to 85.1, and by the addition of 2 ccpand 3 cc. the octane was'increased to 88.2, and 89.7, 39 research method.

The great flexibility of a reforming lsystem as heretofore described, is made apparent by reference to Fig. 2, wherein I have plotted yield in volume per cent as ordinates, and octane numbers, 39 research method, as abscissae. It 4will be observed that the curve 76 at 100% yield shows an octane number of 50.9, the octane number of the original charging stock which includes the light naphtha introduced into the line 15. The system may be operated to produce any desired octane number from 50.9 up to 86, after which the yield decreases so rapidly it becomes inexpedient to run for higher octane numbers. The yield of 80% of 80 octane stabilized gasoline of motor fuel, 10# Reid vapor pressure, as indicated by the broken lines, however, is considerably above that ordinarily achieved by any reforming system of which I am informed.

In accord with my invention, normally gaseous hydrocarbon compounds over and above those usually convertedin the same system when using a compressor are converted into constituents suitable for inclusion in the stabilized gasoline, to a degree which not only accounts for a yield as much as 1% to 2% greater, but alsofor octane numbers of from one to three numbers higher than would be the case without any conversion of gaseous compounds.

As the yield of gasoline decreases with increased octane number by approximately 1% per octane number, 39 research method, it is at once apparent that increasing the octane number of the product by two numbers, due tothe converted gaseous constituents, results in an increase of 4% in yield for a corresponding octane number without such conversion.

In this connection, and in a modified form of my invention, I have introduced hydrocarbons having four carbon atoms per molecule, mostly butane, directly into the stabilizer in place of 'the lighter naphtha. The introduction of the 'butane likewise "increased the yield and'octane number materially over operation Without the added C4 compounds, and by as much as 5% in f. line.

additionally heated by heat exchange.

yield and 1 to 3 octane numbers. State differently, there Was a conversion of the C4 compounds .to as much as 65% to '70% of the amount thereof compounds were introduced, my invention is not ylimited to operations of that character.

More particularly, in accord with a further embodiment of my invention, a full range straight run gasoline, 340 F. end point with an initial of as low as 89 F. (95% recovery) and an octane number of 59.6, 39 research method, was directly charged to the absorber I2. There was produced a yield of 81.5% of 80.0 octane number, 39 research method, 10# Reid vapor pressure, stabilized gaso- Thus this charging stock was increased from its original octane number of 59.6 to an octane of 80.0. In another operation on the foregoing full range charging stock with an increased cracking temperature, there was produced a yield of approximately '70% by volume of stabilized gasoline having an octane number of 86. By the addition of 1 cc. of T. E. L. this octane number was increased to 91.5; by 2 cc., to 93.5; and by 3 cc.

`to 94.7, measured by the 39 research method.

My invention is not limited to naphtha reforming but may be usefully employed for cracking heavier charging stocks such as gas oil. In most cases it is desirable to recycle a portion of the heavier material, which portion may be derived from the bubble tower and in vapor phase., introduced into the superheater coil 22. `The rawcharging stock at a relatively low, or air temperature, is used as the absorbing menstruurn for the absorber i2. The recycle stock because of Vits higher bubble tower temperature is no-t desirable as an absorbing menstruum and is usually In consequence, the total amount of material to be cracked includes the recycle stock which may equal or exceed the raw feed. quirements cannot be satisfied by absorption alone, it may sometimes be desirable to provide a compressor (not shown) for the purpose of elevating in pressure an additional quantity of gas which may be added to the superheater and/or.V

the cycle gas coils.

A study of the foregoing illustrations shows that the separation of the normally gaseous hydrocarbons into rich and lean fractions and the presence in the reaction chamber of the gases.n

absorbed from the lean fraction in mixture with the low octane gasoline results in the conversion of a part of the absorbed gases as well as a part of the rich cycle gas into products suitable for inclusion in the high octane gasoline or motor fuel.

In contrast with prio-r true vapor phase cracking and reforming systems characterized by compressor-circulation of gases, the results achieved by my present invention are equal and evenV Where the gas re-. .1

j or combination of a material portion of the gases fand 5 carbon atoms per molecule.

' superior to said prior systems when operated with all make-gas passing to a catalytic polymerizing unit. This great superiority is the direct result of causing the reforming or cracking reactions to occur under conditions which are substantively different from systems prior to my invention. In the prior true vapor phase reforming system the flash gas had a specific gravity of approximately .865 and the cycle gas a specic gravity of approximately .920, whereas in accord with my invention the absorbed gases have a specific gravity of about 1.41 and the cycle gas a speciiic gravity of about 1.42. In the old compressor type of system a much larger percentage of gases was withdrawnV from the system and they included a larger percentage of hydrocarbons having 3, 4, The higher speciiic gravities of the recycled gases in accord with-my invention is partly the result of the absorption in the absorber of a large proportion of gases richer or heavier than ethane and a relatively small absorption of the ethane and lighter In this Way there is in the reaction zone a higher percentage of less refractory gases which, by reason of their temperature and the particular conditions under which the reaction takes place, in part at least accounts for the surprising conversion of these gaseous products into vconstituents suitable for inclusion in the final product of motor fuel, or high octane gasoline.

The particular conditions under which the reaction takes place substantively differ from the old compressor type of system by reason of the fact that the reaction occurs in the presence of all of the gases made in the system except the small percentage of the light gases Withdrawn from the top of the absorber. The results are superior to those which Would be expected on the consideration alone of the mass action effect of gases. There occurs a conversion or reversion to the end that the total result of the complex f" reactions is the production of a surprisingly small amount of make gas. The internal 'gas cycle is built up to a point where the cycle gas and the 4 absorbed gases bear a weight per cent of between 30%I and 60%V of the fresh feed and there is produced only thatY small proportion of ethane and lighter gases which are withdrawn from the .50

top of the absorber.

My invention further dilers from the compressor' type of system in other important aspects. i First, as above explained, the charge together Vwith the gases absorbed by it is in liquid phase elevated to the desired pressure.

The mixture then ows through the heating tubes Where it is vaporized and thence through the remainder of the reforming system without need for a compressor anywhere in the system. Second, the

overhead'stream from the scrubber-fractionator i is cooled to a greater extent than in the former i compressor system so that a larger percentage of f the normal gaseous constituents are condensed andwithdrawn as a liquid from the accumulator 50. In fact the condensation is adequate to vprovidevfor'the supply of the cycle gas as Well as for the desired vapor pressure of the iinal prodjuct. In liquid formr this condensate is charged to therelatively high pressure stabilizer, around 70" ,300# gauge, and as a result of the larger proportion of condensed normally gaseous hydrocarbons i there becomes available a larger quantity of those normally gaseous hydrocarbons as an overhead gaseous stream from the stabilizer, which gaseous stream forms the supply of the cycle gas. By the very convenient and satisfactory expedient of varying cooling temperature as by controlling the rate of flow of the cooling water through the main condenser 49 by means of valve 48a, the quantity of cycle gas made available in this manner may be controlled as desired and within relatively Wide limits, and preferably so that the combined cycle gas and absorbed gas will always bear the aforesaid weight per cent of from 30% to 60% of the other hydrocarbons present in the reaction zone. As a result of these factors, ease of control of the system as a whole is made possible and any abnormalities incident to operation are readily and quickly corrected. Of equal practical importance is the fact the system as a Whole is simpler in character and less costly.

It will be further observed that the charge, enriched by the absorbed gases, is progressively heated and fiows directly to the reaction zone or chamber and there is eliminated in the case of a totally vaporizable charge, a flash zone or charnber in which new conditions of equilibrium obtain. The intimate mixture of absorbed gas throughout the charging stock is believed to contribute to the complex reactions which appear to take place under conditions which inhibit forma-v tion of normally gaseous compounds which cannot be usefully utilized in motor fuel.

While I have described particular embodiments of my invention, it is to be understood I do not limit myself thereto since many modifications may be made and I therefore contemplate by the appended claims to cover any such modifications as fall within the spirit and scope of my invention.

What I claim is:

1. In a conversion system for hydrocarbons in which a heat carrier heated to a high temperature is utilized to supply heat to hydrocarbons undergoing conversion, the method which comprises cooling and fractionating the reaction products resulting from the conversion of said hydrocarbons, withdrawing a condensate therefrom which includes said heat carrier and products suitable for motor fuel, in an absorption zone utilizing a vaporizable liquid hydrocarbon for absorbing from the gases which were not condensed in said cooling and fractionating operations substantially all of the hydrocarbons heavier than ethane, applying heat to vaporize said liquid hydrocarbons and said absorbed gases and to elevate their temperature to within the range of their conversion temperature during a time interval insufcient for material conversion thereof, separating said heat carrier from said condensate, applying heat to said heat carrier to raise its temperature substantially to within the range of its conversion temperature, during a time interval insufficient for material conversion thereof, commingling all of said heated hydrocarbons, and retaining the commingled hydrocarbons in a reaction zone for the conversion thereof under the aforesaid conditions, whereby only a relatively small amount of products unsuitable for use in motor fuel is produced.

2. In a conversion system for hydrocarbons in which a heat carrier heated to a high temperature is utilized to supply heat to hydrocarbons undergoing conversion, the method which comprises separating from the reaction products resulting from the conversion of said hydrocarbons a vapor stream containing all products suitable for motor fuel and lighter hydrocarbons to be used as said heat carrier, cooling said vapor stream to produce a condensate which includes said heat carrier and said products, in an absorption zone utilizing a vaporizable liquid hydrocarbon for absorbing substantially all of the hydrocarbons heavier than ethane from the gases not condensed by said cooling of said vapor stream, applying heat to vaporize said liquid hydrocarbons and said absorbed `gases and rapidly to elevate their temperature, separating said lighter hydrocarbons from said condensate foi1 use as said heat carrier, applying heat to said heat carrier to raise its temperature for the supply of heat to the hydrocarbons to be converted, commingling all of said heated hydrocarbons, and retaining the commingled hydrocarbons in a reaction zone for the conversion thereof under conditions which produce a relatively small amountof products unsuitable for use in motor fuel. fr

3. The method as set forth in claim 2 in which the quantity of said lighter hydrocarbons utilized as said heat carrier is controlled directly by varying the extent of coolngof said vapor stream.

4. The method as set forth in claim 2 in which the gases absorbed by said liquid hydrocarbon have a specific gravity of about 1.4 and the lighter hydrocarbons forming said heat carrier having a specific gravity of about 1.4.

5. The method set forth in claim 2 in which ethane and lighter gases are withdrawn from said absorption zone, to produce conversion of said commingled hydrocarbons in the substantial absence of said ethane and lighter gases. H,

6. The method of reforming gasoline of low octane number into gasoline of high octane number in the substantial absence of all gaseous products lighter than propane, which comprises separating from said reformed products a vapor stream containing said high octane gasoline and lighter hydrocarbons, cooling said vapor stream to produce a condensate which includes said high octane gasoline and normally gaseous hydrocarbons to be used as a heat carrier, in an absorbing zone utilizing said low octane gasoline for `absorption of uncondensed gases of hydrocarbons heavier than ethane, applying heat to the mixture resulting from the absorption to vaporize it and to elevate its temperature to within the range of its reforming temperature, separating said lighter hydrocarbons from said high octane gasoline by application of heat and fractionation, applying heat to said lighter hydrocarbons to elevate their temperature above the temperature of said mixture and to form said heat carrier therefor, commingling said heat carrier and said mixture to produce conversion in vapor phase of normally gaseous and liquid constituents to said high octane products suitable for inclusion in motor fuel, and withdrawing ethane and lighter gases as substantially the only gases withdrawn from the reforming operation. l

'7. A method of converting hydrocarbons in vapor phase in the substantial absence of all gaseous products lighter than propaneA resulting from the conversion reactions, and characterized by the use of a gaseous heat carrier, which comprises separating `from the reaction products a vaporous and gaseous stream containing all products suitable for use as motor fuel and lighter products, cooling said stream to produce a condensate which includes said products suitable for motor fuel and normally gaseous hydrocarbons in quantity adequate for use as said heat carrier, in an absorbing zone utilizing vaporizable liquid hydrocarbons to absorb from the gases not condensed by said cooling operation substantially all Vof the hydrocarbons heavier than kethane,

applying heat to the mixture of said liquid hydrocarbonsl and their absorbed gases to vaporize the same and to elevate the temperature thereof to Within an approximate conversion temperature during a time interval insuflicient for material conversion to occur, concurrently separating said heat carrier from said condensate, applying heat to said heat carrier to raise its temperature materially above said temperature of said mixture, and commingling said heat carrier with said mixture to produce simultaneous conversion of all of said commingled hydrocarbons.

8. In a system in which vaporizable liquid hydrocarbons undesirable as motor fuel are in vapor phase in a reaction zone thermally converted into products valuable for motor fuel, the method which comprises separating from the products from the reaction zone a vapor stream containing all of said valuable products and all lighter products, by controlled condensation of said vapor stream producing a condensate containing said valuable products and a desired amount of lighter hydrocarbons to be used as a heat carrier, utilizing the charge of said undesirable liquid hydrocarbons for absorption of uncondensed gases of substantially all hydrocarbons heavier than ethane, withdrawing from the system said ethane and lighter hydrocarbons, heating and fractionating said condensate to separate said heat carrier therefrom, separately and concurrently applying heat to said heat carrier and to said gas-enriched charge respectively to elevate them to Within the ranges of their conversion temperatures, during time intervals insufficient for material conversion to occur, in said reaction zone commingling said heat carrier and said gas-enriched charge for their conversion in the substantial absence of ethane and lighter gases into said valuable products.

9. The method as set forth in claim 8, in which the quantity of heat carrier is controlled directly by varying the extent of cooling of said vapor stream, and in which the Weight per cent of said heat carrier and of said absorbed gases is maintained between 30% and 60% of the remaining hydrocarbons in said reaction zone.

10. Themethod as set forth in claim 8, in which specific gravities of said heat carrier and of said absorbed gases are approximately equal to 1.4 and in which they form a weight per cent of between 30% and 60% of the other hydrocarbons in said reaction zone.

11. In a vapor phase cracking system in which a heat carrier consisting f gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with charging stock uncondensed gases made during said cracking for absorption of a substantial quantity of said gases, heating said enriched charging stock to convert the same into said stream of heated vapors, commingling therewith said heat carrier at a temperature which induces rapid cracking of said vapors, fractionating and cooling said reaction products to produce a condensate and said uncondensed gases, returning said gases for said contact with said charging stock, in a separating zone removing from said condensate lighter constituents, heating said lighter constituents to a high temperature to form the source of supply of said heat carrier, said cooling of said cracked products being sufcient to condense said lighter constituents in quantity adequate for the supply of said heat carrier, and removing from said separating zone a stabilized product suitable for use as motor fuel.

12. In a vapor phase cracking system in which a heat carrier consisting of gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with charging stock uncondensed gases made during said cracking for absorption of from %.to 50% of said gases, heating said enriched charging stockV to convert the same into said stream of vapors, commingling therewith said heat carrier gas at a temperature and in quantity sufcient further to elevate the temperature of said stream of vapors to produce rapid cracking thereof, fractionating and cooling the reaction products to produce a condensate consisting of motor fuel and lighter hydrocarbons having from 3 to 4 carbon atoms per molecule, returning the uncondensed gases for said contact with said charging stock, elevating said condensate to a superatmospheric pressure of the order of 250 to 300 lbs. per square inch, in a zone maintained under said high pressure removing from said condensate the larger part of said lighter hydrocarbons, heating said lighter hydrocarbons to said high temperature to form the source of supply of said heat carrier gas, and removing from said high pressure zone a stabilized product suitable for use as motor fuel.

13. In a vapor phase cracking system in which a heat carrier consisting of normally gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with a heavy naphtha charging stock, the lighter gases made during said cracking for absorption of a substantial quantity of said gases, heating said enriched charging stock and producing therefrom said stream of vapors, commingling therewith said heat carrier at a temperature quickly to further elevate their temperature and to induce rapid cracking thereof, fractionating and cooling said reaction products to produce a condensate consisting of motor fuel and normally gaseous hydrocarbons, returning the lighter uncondensed gases for said contact with said heavy naphtha chargingr stock, elevating said condensate to a high pressure, in a zone maintained under said high pressure removing from said condensate said normally gaseous hydrocarbons, concurrently introducing into said zone of high pressure a stream of light naphtha, removing from said light naphtha lighter constituents thereof, withdrawing from said high pressure zone said gaseous hydrocarbons and Said lighter constituents, under the applied pressure from said high pressure zone heating them to a high temperature to form the source of supply of said heat carrier, and removing from said high pressure zone a stabilized liquid product suitable for use as motor fuel.

14. In a vapo; phase cracking system in which a heat carrier consisting of normally gaseous hydrocarbons iscommingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with a heavy naphtha charging stock, uncondensed gases made during said cracking for absorption of a substantial quantity of said gases, heating said enriched charging stock and producing therefrom Said stream of vapors, commingling therewith said heat carrier at a temperature quicklyto further elevate their temperature and to induce rapid cracking thereof, fractionating and cooling said reaction products to produce a condensate consisting of motor fuel and normally gaseous hydrocarbons, returning the uncondensed gases for said contact with said naphtha charging stock, elevating said condensate to a high pressure, in a zone maintained under said high pressure removing from said condensate said normally gaseous hydrocarbons, concurrently introducing into said zone of high pressure a stream including light hydrocarbons having about four carbon atoms per molecule, witlidrawing from said high pressure zone said light and said gaseous hydrocarbons, under the applied pressure from said high pressure zone heating them to a high temperature to form the source of supply of said heat carrier, and removing from said high pressure zone a stabilized liquid product suitable for use as motor fuel.

15. In a vapor phase cracking system in which a heat carrier consisting of normally gaseous hydrocarbons is commingled with a stream f heated hydrocarbon vapors to pro-duce cracking thereof, the method which comprises countercurrently contacting with a heavy naphtha charging stock, uncondensed gases made during said cracking for absorption of a substantial quantity of said gases, heating said enriched charging stock to produce therefrom said stream of vapors, commingling therewith said heat carrier at a temperature quickly to further elevate their temperature and to induce rapid cracking thereof, fractionating and cooling said reaction products to produce a condensate consisting of motor fuel and normally gaseous hydrocarbons, returning the uncondensed gases for said contact with said naphtha charging stock, elevating said condensate to a high pressure, in a zone maintained under high pressure removing from said condensate said gaseous hydrocarbons, concurrently introducing into said zone of high pressure a stream of light hydrocarbons having about four carbon atoms per molecule, withdrawing from said high pressure zone said light and said gaseous hydrocarbons, under the applied pressure from said high pressure zone, heating them to a temperature high enough to induce said rapid cracking, said light and gaseous hydrocarbons forming the source of supply of said heat carrier, and removing from said high pressure zone a stabilized liquid product of high octane number and suitable for use as motor fuel.

16. In a vapor phase cracking system the method of operating the system without a compressor which comprises fractionating and cooling the reaction products to produce a condensate within the gasoline range and which includes a substantial proportion of lighter hydrocarbons having three to four carbon atoms per molecule, removing the uncondensed gases, elevating the pressure upon said condensate and transferring it to a high pressure zone, stripping from said condensate said lighter hydrocarbons and by said pressure flowing them through a heating zone, in said heating zone transferring heat to said lighter hydrocarbons to raise their temperature to above 11.75 F., countercurrently contacting with charging stock said uncondensed gases for the absorption by it of a considerable quantity of said applying heat to said enriched charging stock to raise it to a vaporization temperature, the presence of said absor ed gas reducing the partial pressure for complete vaporization thereof, applying heat to raise to a temperature above about 850 F. a stream of vapors at least in part mingling said heated hydrocarbons and said heated vapors to produce cracking thereof, and subjecting the reaction products to said frac-- tionating and cooling operations as aforesaid.

17. In a Vapor phase cracking system characterized by a maximum operating p-ressure of less than 300 lbs. per square inch, the method of operating the system without a compressor and with circulation of relatively large quantities of gas therethrough which comprises fractionating and cooling the reaction products to produce a condensate within the gasoline range and which includes a substantial portion of lighter hydrocarbons having 3 to 4 carbon atoms per molecule, separating the uncondensed gases from said condensate, elevating the pressure of said condensate and transferring it to a high pressure zone, in said zone stripping from said condensate said lighter hydrocarbons, utilizing said high pressure to produce flow of said lighter hydrocarbons through a heating zone, in said heating zone transferring heat to said lighter hydrocarbons to raise their temperature to above 1175 F., countercurrently contacting with charging stock said uncondensed gases for the absorption by it of a large quantity of said gases, applying heat to said enriched charging stock to raise it to a Vaporizing temperature, the presence of said absorbed gas reducing the partial pressure of said charging stock, further elevating the temperature of said vapo-rized charging stock and gases to above about 850 F., commingling said heated hydrocarbon-'s and said heated vapors and gases to produce cracking thereof and conversion of both charging stock and gases and gaseous hydrocarbons into products suitable for inclusion into motor fuel, and subjecting said reaction products to said fractionating and cooling operations as aforesaid.

18. In a vapor phase cracking system in which a heat carrier consisting of gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with a charging stock uncondensed gases made during said cracking for absorption of substantially all of the hydrocarbons heavier than ethane, heating said charging stock together with gases absorbed therein to convert the same into said stream of heated vapors, commingling therewith said heat carrier at a temperature which induces rapid cracking of said vapors, fractionating and cooling the reaction products to produce a condensate and said uncondensed gases, returning said gases for said contact with said charging stock, in a separating zone removing lighter constituents from said condensate, heating them to a high temperature to form the source of supply of said heat carrier, and a predetermined time after mixture of said heat carrier with said stream of heated vapors terminating the cracking reactions by rapid cooling of the reaction products. v

19. In a vapor phase cracking system in which a heat carrier consisting of gaseous hydrocarbons is commingled with a stream of heated hydrocarbon vapors to produce cracking thereof, the method which comprises countercurrently contacting with charging stock uncondensed gases made during said cracking for absorption of substantially all of the hydrocarbons heavier than ethane, withdrawing from said absorption zone and from the cracking system the unabsorbed gases, heating said charging stock together with gases absorbed therein to convert the same into derived from said charging stock, and comsaid stream of heated vapors, commingiing therewith said heat carrier at a temperature which induces rapid cracking of said vapors, fractionatand cooling the reaction products to produce a condensate and said uncondensed gases, returning said gases for said contact with said charging stock, in a separating Zone removing lighter constituents from said condensate, heating them t0 a high temperature to form the source of supply of said heat carrier, and a predetermined time after mixture of said heat carrier with said stream of heated vapors terminating the cracking reactions by rapid cooling of the reaction products, the Withdrawal of unabsorbed gases from said absorption zone producing conversion of said commingled hydrocarbons in the substantial absence of ethane and lighter gases.

FRANK H. PRAEGER.

Images