US1920929A - Process for cracking petroleum hydrocarbons - Google Patents

Description

Aug. 1, 1933. WLM, CROSS 1,920,929

PROCESS FOR CRACKING PETROLEUM HYDROCARBONS Filed May 9. 1929 IN VENT OR h/aizer/Y. 6105.5.

"Patented Aug. 1, 1933 PrsoFHcE PROCESS 'FOR CRACKING PETROLEU HYDROCARBONS v 'Walter M. Cross, Kansas City, assignor to Gasoline Products Company, Inc., New York,

N. Y., a Corporation of Delaware Application Mayl), 1929. Serial No. 361,632

2 Claims.

This invention relates to improvements in the vprocess and apparatus for, cracking petroleum hydrocarbons and refers more particularly to a process in which the oil, after being brought 5 rapidly to a cracking temperature, is maintained throughout the necessary time period to con- ,summate the cracking at temperatures substantially at or slightly below the cracking temperature, The novelty in the invention lies primari- .1y in the maintaining of the oil in the Zone of reactionat temperatures not to, exceed 100 F. T I

"used, either powdered coal, oil, gas, or a mixbelow the cracking temperature or at temperatures sufficiently high to prevent the agglutina tion of the chemical; condensation products formed in theioil.

The process also offers an operation by means j ,of which carbon troubles usually accompanying oil crackingfare substantiallyeliminated because the g chemical condensation products formed,

. .whichconsist of small'globular bodies, are held insuspension in the liquid, coursing through the apparatus and thisliquid is traveling at asufficient velocity and with turbulence which maintains any separated bodies suspension in, the .Zi hydrocarbon menstruumL Fig. 1 is adiagrammatic showing of the apparatus in which the process may be carried on.

Referring to the drawing: at 1 is shown a furnace divided into compartments 2 and 3 by 3 a bridge wall 4., 2 Upon the sides and ceiling of *the compartment 2 are arranged heating tubes which are subjected to the heat of the combustion gases produced by burning fuel by meansof a burner 6. In the adjacent compart- 3 ment 3 is a bank of tubes 7 which are subjected to convection heat of the combustion gases passing over the bridge wall 4.

It will be noted that the cracking tubes in the chamber 2 are subjected primarily to radiant 4 heat energy, while the bank of tubes 7 receives principally convection heat. The tubes 5 arrangedupon the reflecting surfaces of the compartment'Z and on the ceiling of compartment 3 are connected inc'series to form a continuous -coil.- These tubes are connected by atransfer 7 line 8 to the tube bank 7.

Connected to thedischarge end of the tube bank 7, by means of atransfer. line 9, is evaporator 10: interposed in the transfer line 9 is a pressure'reduction valve 11. The. evaporator has a liquid draw-off line 12 at the bottom, controlled by a valve 13. vaporized overhead material' passes off through the pipe 1; and is'introduced near the bottom of the bubble tower 15.. ,The' bubble tower, or fractionator, has a gas relief line 24', regulated by a valve 25 and a liquid draw-01f line 26,-controlledby a Valve 27.

In the furnace any suitable type of fuel is ing purposes, including kerosene, gas oil, fuel oil,

or derivatives thereof, is supplied through the pipe 38'and is circulated through a preheating coil 3%,"positioned in the upper part of the hubble tower. The preheated oil is then directed by means-of a pipe 35 to the cracking tubes 5,

positioned in the chamber 2. In the cracking tubes, the oil is raised rapidly to a crackingtemperature so that, on being discharged from the cracking tubes through the'discharge line 8, the

temperature has been raised to 7001000 F.,

depending upon the character of the oil undergoing treatment and the time allowed for cracking. The relation of the heating surface of the radiant tubes designated as 5 in the drawing to the convection bank designated as 7 is approximatelyas 2-1. Also the tubes in the convection bank are arranged sothat the oil, in tray- 'eling therethrough, passes in adirection con-v currently to the direction of the combustion gases, that is, from the top downwardly.

After passing through the reaction tubes, or convection bank, the oil is discharged through the pipe 9 into the evaporator. At the valve 11 the pressure is reduced and, vwith this reduction of pressure, there is a separation of vapors and liquid, due to the contained heat in the oil and 1 the pressure reduction. At a point near the, discharge of the convection bank is a pipe connection 36 by means of which a cooler medium may be introduced from any convenient extraneous lated, by means of the pump 39, tothe cracking tubes 5. The heavy liquid uneva'porated in the container 10 is drawn on through the pipe 12 and divertedto fuel oil storage. 7 r

The overhead material fromthe bubble tower" is passed through the condenser 20 and'collected as distillate and gas in the separator 23 where proper separation of the constituents is effected.

The amount of reflux condensate or'recycle stock returned from the bubble tower to the cracking tubes is determined by the amount of dephlegmation necessary which, in turn, is delpendent'lupon the character of the oil undergoing treatment.

, The temperaturecontemplated in the crackjingtubes ranges ,iljom TOW-1000" F., the maximum' temperature being" attained in the discharge or transfer line 8 which connects the ratubes'or cracking tubes with the convection bank or reaction tubes. In the reaction zone, which constitutes the convection bank of tubes 7, the temperature is notpermitted tofall more than 100 below'the maximum temperature in the cracking tubes 5. .This'decrease in "temperature '0: approximately 100 has been 'found t'o' be approximately the decrease in temperature which has no particular effect upon'the agglutination or combination of the molecular particles .of the condensation product accumulating in the oil during the cracking reaction. ..'The chemical condensation products formed during the cracking operation consist of small globularbodies' held in suspension iri'the liquid iffcracking stock as it courses throughjthe tubes f the cracking apparatus. "males, at the beginning of the cracking, are

These globular relat'ively sparsely scattered through the oil and, "as the oil-cracking proceeds by longer exposure to the cracking temperature, they become more and 'more abundant but,'under the high temperaturesImaintained, do not readily stick together nor have a tendency to agglutinate. Since thejtemperature of the oil in which they float or are heldin suspension remains ator slightly below. the temperature at which these condensation products were formed, the particles seem to re- 1 main as separate"erititiesjand'have no tendency Ttoag'gluti nate or. stick together. The temperatui e may not, however, be decreased materially more' 'than 100 before there is perceived an im-' (mediate tendency upon the part of the particles to accumulate.

The particles as formed are so small that it is necessaryto see them, witha high powered microscope and,when viewed in this manner, have a'decidedBrownian movement The decrease in temperature necessary to cause the particles to Iagglutinat'e or become sticky and have a tendency to adhere to one another differs somewhat with thedifierent oils and somewhat with the temlperatures necessary to crack the'particular types for oils/ 1f the temperature is reduced from '5 slightly below the range, which is approximately 100, these condensation productsbecome sticky and thelittle globular "bodies composing them gradually adhere to one another until their molecular weightis such that they are deposited or settle on to the container in which the oil is being held, or through which it is being passed.

In normal cracking operations utilizing heating coils and a separating or reaction chamber, the reduction in temperature'in the separating chamberis materially in excess of 100; consequently there is a rapid formation or accumulation of the hydrocarbon condensation products and considerable quantities of these condensation productsare deposited.

The condensation products mentioned above are formed and are deposited in the usual cracking operation, and are ordinarily known in the petroleum industry as carbon; but it is not really atrue carbon, but is' a chemical condensation product which has 'a very high percentage of carbon and a low percentage of hydrogen in its molecules and also has a relatively high molecular weight.

In the present process, after the cracking operation and reaction period have been completed,

ing of the cracking oil during the reaction or cracking periods. As suggested, at the end of the reaction'period or time thereis provided a means of sudden" chilling of'the oil to temperatures in excess of 250 and normally 350 or more below the'cracking temperature. The cooling and accompanying vaporization produce violent agitation andthere is not sufllcient time allowedfor any agglutination of the particles to occur while'the actual cooling takes place, thus theglobular particles will not adhere to each other and become sufliciently heavy-to settle out. While it is not possible to prevent all agglutination or'accumulation of the separate particles, it can be prevented to such"- an extent that a cracking plant may be operated for ninety days or more,jcomp'ared with the normal ten day period when this agglutination of the particles is allowed to take placein a relatively "quiescent pool of oil and particularly when the temperature of the M1 Inasmuch as in many very successful cracking processes, the time required for cleaning the apparatus, including the settling tanks, etc. may occupy as much at 10-20% of the total operating time, whereas in this method the cleaning operation may readily lee-reduced to 1-2% of the total operating time, the present process offers a very great saving,particularly in view of the fact that the typeof apparatus used maybe constructed with considerable less expenditure than where large separators or reaction chambers are supplied. The pressure maintained upon the cracking and reaction zones rangesfrom 500-1000 pounds per square inchand, under normal operation the pressure -will be maintained "at from 700-900 pounds, 'so'that a substantial portion or the oil passing through the system is maintained in the liquid phase.

The addition of acooling medium, such as hydrocarbon, in the reaction zone, near the outlet thereof, is to facilitate and increase the rapidity with which cooling of theoil is carried on with a reduction of pressure. The introduction of .a cool hydrocarbon near the discharge of the reaction period reduces the temperature below that point at which stickiness, in the hydrocarbon particles is produced. The fact that these particles can be p more or less rapidly frozen within the oil body so that they remain in a very finely dispersed condition with no tendency towards agglutination e1im-' inates from the operation carbon difiiculties which are inherent to liquid vapor phase cracking processes in use at thepresent time. a

I claim as my invention: v

1. A process of cracking hydrocarbon oil com-- prising the steps of passing oil 'through'a section of a continuous coil in a heating zone, efiecting combustion for said heating zone and subjecting the oil during substantially its entire travel through said section of the continuous coil to the radiant heat of combustion whereby it is rapidly v brought to a cracking temperature, then passing the oil through another section of the coil in a second heating zone where it is subjected to convection heat from combustion gases derivedfrom said first heating zone controlled to maintain the oil at a cracking temperature lower than the cracking temperature attained by it in said first heating zone, then passing the oil through another section of the coil in the second heating zone where the temperature of the oil is rapidly decreased by the introduction of a cooling medium into the oil, and removing and vaporizing the oil.

2. A process of. cracking hydrocarbon oil com-- I prising the steps of passing oil'through a section of a continuous coil heating zone, eifecting combustion for said heating zone and subjecting the oil during substantially its entire travel through said section of the continuous coil to the radiant heat of combustion whereby it is rapidly brought densation products formed during cracking from agglutinating, then passing theoilthrough another section of the coil in the second heating zone where the temperature of the oil is rapidly decreased by the introduction of a cooler hydrocarbon oil into the oil and removing and vaporizingv the oil. I

WALTER M. CROSS.

Images