US2046501A - Process for the pyrolytic decomposition of hydrocarbons - Google Patents

Description

M. B. COOKE July '7, 1936.

PROCESS FOR THE PYROLYTIC DEcoMPosITIoN oF HYDRocARBoNs Filed March 12, 1952 mw ESS lull 1 u Patented July 7, 1936 PATENT orties PROCESS FOR THE PYROLYTIC DECOM- POSITION HYDROCARBONS Maurice B. Cooke, New York, N. Y.

Application March 12, 1932, Serial No. 598,503

1 claim.

A My invention relates to a process 'for the pyrolytic decomposition of hydrocarbons to form Y gasoline-like hydrocarbons suitable for using as a motor fuel having high. antiknock qualities. The process is usually known as a cracking process and relates more particularly vto the cracking of hydrocarbons in the vapor phase by hot gases of combustion.

When fuel is burned with no excess of air, the temperature of combustion is between 3,000 and 4,000 F. These temperatures are too high for eiiicient cracking and accordingly they must be tempered or brought down to about 1,500 F. in order to give an efficient crackingprocess.

In an application of William O. Keeling, Serial No. 586,573, a m'ethod of tempering "the combustion gases by means of a'cooler, inert Vgas is disclosed.

Y This application relates to an improvement in my copending application Serial No. 598,502, filed March 12, 1932 now patent No., 2,016,798 issued October 8, 1935 to Maurice B. Cooke.

' When a great volume of gas is introduced into the fractionating tower, many disadvantages result. The equipment must be made a larger size. The volume of gas to be compressed for absorption purposes is so increased that the process becomes expensive. The use of a cool, inert gas to temper the combustion gases represents aV direct loss of heat besides increasing the volume of the gases tobe handled.

One object of my invention is to avoid the disadvantages above pointed out, with special reference to reducing the volume of the gas to be handled by Vthe'fractionating equipment.

It Will be noted that the instant invention differs from my above mentioned co-pending ap' plication in that all the vapors,gases and the like emanating from the reaction zone are cooledand condensed and the ilxedy gases are to be removed therefrom. The condensed material is to4 be reheated and passed tothe fractionating zone where the gasoline-like hydrocarbons are vseparated from the gas oil andotherheavier hydrocarbons. Y

A further object of my invention is to provide a process in which fractionating equipment of small dimensions may be used due to the fact that no considerable amountof ue gas or xed gas passes through' the fractionating zone.

Another object of my invention is to provide a process in which the hot gases of combustion are tempered by means of heatexchange.

A further object of my invention is to employ o the gas heat for topping the charging stock,`va

porizing the charging stock for conversion into Y the vapor phase and supplying heat forjother purposes such as distilling the oil or the generation or high superheating of steam.

Still another object of my invention is to provide a vapor phase cracking process in which hot gases of combustion are used to supply the cracking heat which is exible of control and efficient in operation.

Still another object of my invention is to check the reaction to prevent over-cracking by means of shock chilling the products of reaction.

Other objects of my invention will appear from the following description:

The figure shows a diagrammatic View of one embodiment of the process of my invention.

In general, my invention consists in burning fuel and air with surface combustion in a furnace to supply hot gases of combustion substantially devoid offree oxygen. I charge crude oil from storage to suitable heat exchangers through a coil situated within the furnace.A The temperature oi' the hot gases of combustion will be lowered and lose part of their heat in heating the incoming charge during its passage through the topping heating coil. 'Ihe heated products are discharged into a fractionating tower` preferably of the bubble type, whence the vapors are withdrawn o-verhead, condensed and passed into a separator. The gasoline iswithdrawn from the separator and passed to storage. A heavier fraction collects in the separator and is refluxed into the bubble tower. The reux condensate from the bubble tower may be pumped to storage andforms the cracking stock which is used in my process.' The reuX condensate may, if desired, be pumped directly through suitable heat exchangers into an accumulator tank. Oil is pumped from the accumulator tank through suitable heat exchangers', through a second coil situated in my furnace where the heat necessary to convert a substantial portion of the charging stock into vapors is supplied. The heated charging stock is passed into a flash evaporator whence the vaporsu arewithdrawn and passed to the cracking zone. In'the cracking zone the vaporized hydrocarbons encounter the hot gases of combustion which have been tempered to about 1,500 F. The hot gases of combustion admixing with the vapors bring the mixture to about 1,100 F. at which temperature cracking takes place rapidly. The increase in volume is accommodated for by a progressively increasing cross sectional area. After leaving the cracking zone, the products of the reaction'are shockl chilled by means ofv an oil'spray.

The products, after being chilled, pass into a tar separator. The tar laden quenching oil is drawn through a cooler and pumped to storage and may be used for fuel oil. The vapors and gases are passed through a sectional entrainment condenser through suitable heat exchangers and into a separator, whence the uncondensed gases are withdrawn overhead and allowed to pass into the gas main. It will be noted that this is the novel step in which the excess and uncondensed gases are withdrawn from the system in order to pre- Vent their being passed through the fractionat- The condensate is then pumped` in,

ing tower. heatv exchange with the hot products to revaporize the condensate and in vapo-rized condition itis passed into a fractionating tower. The entrain; ment condensate from the condenser collects in suitablepockets and may be passed Veither into the separator or into a fractionating tower depending upon their nature and character.

The reflux condensate from the fractionating tower is withdrawn and pumped through a cooler in order to reduce the temperaturethereof to render it suitable as a quenching medium. After passing through 4the cooler, it is passed through the sprays in order to be used inthe chilling zone. A portion of the reflux condensate from the fractionating tower may be diverted into the accomulator for recycling. The vapors withdrawn from the fractionating tower are cooled and passed into a separator from which the water is withdrawn. The uncondensed vapors from the separator are compressed and cooled and passed into a receiver. The condensate is withdrawn as gasoline and passed to storage.

More particularly, referringV nowto the drawing, the crude oil from storage is charged through lline I andpumped by pump 2'. through heat exchanger 3,'through heat exchanger 4,.through topping heating coil 5, where the crude oil being charged is heated.. The heat imparted to them-.- coming crude lowers the temperature of the .combustion gases. The oil leaves the topping. heating coil through line E and is charged into the fractionating tower 1. 'This tower is preferably of the bubble type but it is to beunderstood that any suitable fractionating column may be' employed. The topped oil is withdrawn .through line 8 and pumped by pump 9 through heat .exchanger 4. If valve I0 be closed, and valve Il be opened, the oil will pass through cooler, I2 into storage I3. The cooler I2 is cooled by circulating water or any suitable means.Y The pump I4 will pump oil from the cracking stock storage Ytank I3 if valve I5 be open. Ifvalve- Ii!r be open and valve II closed, the topped crude will pass through line I 6 into line I1 topump I4. v Thevapors from the bubble4 tower 1 arewithdrawn through line I 8, through heat exchangerv 3 into cooler I9 where ii:` is condensed. The condensate passes through line 2Q into separator 2l. The gasoline isrwithdrawn through line 22 vand passed to storage. A heavy fraction is withdrawn Y from the separator through line 23 by pump 24 Y and pumped back into the bubble tower 1 Vas a reflux. The topped crude is pumped by pump I4 through heat exchanger V25; through heatexchanger 21, whence it passes through line 28into the accumulator 29. The charging stock Athus preheatedl is withdrawnV through line 30 by pump 3l and is pumpedrthrough line 32. The products of combustion in the furnace are tempered by losing some of their heat to thechargingf'stock passing through coil 40. .The Yheated charging stock leaves the vcoil 40 through line 4I and passes into the ilaSh evaporator 42. The unvaporized oil from the Hash evaporator may pass through line 43, through valve 44, through line 41, through cooler 49, where it is pumped by pump 59 to 1, pressor 55 into gas supply tank 56, whence gas is mth-drawn through line 51 being controlled by valve 58 into the mixing chamber 59 of a surface combustion burner. Compressed air, controlled by valve 6I', also passes into the mixing chamber 59. The mixture burns with surface combustion about the refractory granules 62, ofthe surface combustion burner 63'.. The hot gases of combustion will pass into the furnace 64 andy be tempered by heat exchange.

with the material passing through coils 4B and. 5 respectively and into the mixing zone 52,

`whence acommingling of the hot products of combustion so tempered to about 1,50011'. Vwill takeplace withthe hydrocarbon vapors coming from the flash evaporator 42,v After admixture, the temperature will be about 1,100 F. and cracking f or pyrolytic decomposition will take place rapidly. y

Ascracking takes place, the volume of the products vwill increase and, in order to prevent the building up of pressure, a cracking chamber of progressively increasing volume is provided. Inasmuch as the cracking will take place very rapidly, at the temperature of '1,050 YF., I resort to shock chilling or quenching tov reduce the temperature of the products of reaction from 1,100? F. tor'100"Y F. -I do this by means of oil sprays 53',A 54', and 562 oil spray 5B' being located in the -tar separator 51. The temperatureof F. is low enough vto prevent any further reaction and high enough to permitthe distillate to es- 'cape'inl the vapor state into the fractionating tower. The heavy,'tarry fuel oil, however, will the condensate which inturn will be heated. The

condensate is allowed to collect in compartments 60, 6I and 62. The condensate may be withdrawn from theV respective .compartments and selectively passed into the-separatorV or frac- -tionating tower through lines 63 and B4 respectively. The entrainment condensate may be sup#V plied as desired by means of valves 65, 66, 61 j and 68, so that all or part of the condensate collected in the sectional entrainment condenser 31 may be passed to either the'fseparator or the fractionating tower as desired and depending upon the nature of the condensate. "The vapors leave the sectional entrainment condenser through line' 69 land Kpass through heat exchanger 34, through cooler 35 and into separator 33. The uncondensedgases escape from the separator 33, through line 38 fand'pass into gas main 53. .The condensate is pumped from the separator 33 by pump 39 through line 45 through heat exchanger 34 through line 46 through the tubing 36 of the sectional entrainment condenser 36 where the heat of the vapors coming through 59 will revaporize the condensate. It will be appreciated that by withdrawing the fixed gases before the fractionating. tower that I may use fractionating equipment of smaller dimensions and am enabled further to eliminate the expense of compressing a large quantity of g-as during gasoline absorption treatment.

The vaporized condensate passes through line 48 into fractionating tower 1U.

The reux condensate from the fractonating tower is withdrawn through line 1I and passed through heat exchanger 21, through line 12, through pump 13, through cooler 'I4 and through line l which terminates in a manifold for the quenching sprays. The quenching oil leaves line 15 through valve controlled lines Tl, 18 and 80. If desired, a portion of the bottom from the fractionating tower may be diverted through valve controlled line 8| and allowed to pass into the accumulator for recycling.

The vapors from the fractionating tower pass through line 82, through heat exchanger 25, through cooler 83, through line 84 into separator 85. The Water condensed from the stripping steam is withdrawn through line 8B. The gasoline-like hydrocarbons are withdrawn through line 81 and passed to storage. The uncondensed vapors from the separator will contain a quantity of gasoline-like hydrocarbons. Accordingly, I propose to withdraw it through line 88 and compress the vapor in compressor 89, pass it through cooler 90 into receiver 9|. The cooling and compressing will precipitate gasoline-like hydrocarbons which are withdrawn through line 92 and pass into line 81 to storage.

It will be appreciated that my process has many advantages. I temper the hot products of combustion by means of heat exchange and use the heat obtained by tempering to perform useful steps in my process. The thermal eicieney of my process will be exceedingly high. The exibility of control is manifest. The temperature of the combustion gases, the temperature of the quenching oil and hence the temperature of reaction may be controlled within close limits. I am enabled by my process to crack hydrocarbon oil inthe vapor phase and obtain a gasoline-like hydrocarbon suitable for tuse as a motor fuel and having an exceedingly high an- A hydrocarbon oil which is not in the vapor form to be present.

This insures the absence of the danger of the formation of coke or carbon deposits within my cracking zone. It will be understood, of course, that suitable lagging is pro- Vvided throughout the piping and the piece of apparatus used in my process to prevent the loss of heat by radiation. By withdrawing a large quantity of the gas from the system before fractionating the products of combustion, I am enabled to avoid large fractionating equipment and to dispense with the necessity of treating a disproportionate amount of gas in gasoline absorption treatment.

It will be understood that certain features, subcombinations and operations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claim. It is further obvious that various changes may be made in details within the scope of my claim without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specic details shown and described.

By this method of cracking hydrocarbons in the vapor phase, in which the hydrocarbons are combined with the combustion gases, the latter being maintained at selected, controlled temperatures of reaction, a motor fuel having a high octane number and high antiknock value is obtained. The process eliminates parasitic cracking which accompanies conventional cracking methods, in which the hydrocarbons are converted in tubular containers and heated by external circulation of the combustion gases there about. The intimate mixture of the combustion gases with the hydrocarbon vapor produces a distribution of heat impossible with the conventional tubular cracking processes.

Having thus described my invention, what I claim is:

The process of treating hydrocarbon oil to form hydrocarbons of lower molecular weight which includes the steps of generating hot combustion gases, passing relatively heavy oil charging stock in indirect heat exchange with said hot combustion gases to reduce the temperature thereof, subjecting the relatively heavy oil charging stock thus heated to a topping oper-ation, passing the topped oil as the hydrocarbon oil to be cracked, in indirect heat exchange with said combustion gases to lower the temperature thereof, flashing the oil thus heated into vapors in a vaporizing stage, directly commingling said vapors with said tempered products of combustion, permitting a pyrolytic decomposition of said hydrocarbon vapors to take place to form hydrocarbons having a lower molecular weight, and stopping said reaction by spraying cooler quenching oil into the reacting vapors after the reaction has progressed a desired extent whereby over-cracking is prevented, cooling the products of reaction, separating the uncondensed xed gases from the condensate in a separating stage from which the uncondensed xed gases and condensate are separately withdrawn, revaporizing the condensate, fractionating the vapors in a fractionating stage, and withdrawing reflux condensate from the fractionating stage for use as the quenching oil.

MAURICE B. COOKE.

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