US2160875A - Cracking hydrocarbon oils - Google Patents

Description

Patented June 6, 1939 UNITED STATES PATENT OFFICE CRACKING HYDROGARBON OILS poration of Delaware Application March 24, 1936, Serial No. 70,628

4 Claims.

This invention relates to the manufacture of gasoline of superior anti-knock quality and contemplates a unitary process in which higher-boiling oil is converted into lower-boiling oils within the gasoline boiling-point range and gasoline constituents of insufliciently high anti-knock quality are subjected to reforming to increase the antiknock quality thereof.

The invention is particularly adapted for the processing of heavy stocks, such as reduced crude or crude petroleum containing large proportions of heavy residual constituents. In accordance with the invention, heavy or highly viscous stocks may be subjected to moderate conditions of cracking to effect viscosity breaking of the stocks and to thereby form relatively large quantities of gas oil or intermediate constituents adapted for high temperature cracking anda smaller proportion of gasoline, which, due to having been formed under viscosity-breaking conditions, may be of relatively inferior anti-knock quality. The gas oil or intermediate constituents may be subjected to hightemperature cracking conditions conducive to the formation of gasoline constituents of high anti-knock quality, and the relatively low antiknock gasoline constituents derived from the viscosity-breaking operation may be subjected to reforming to increase the anti-knock quality thereof.

An important feature of the invention consists in taking a heavy fraction derived from the viscosity-breaking operation, such as a residue or a heavy condensate produced in fractionating the viscosity-broken products, and bringing such heavy fraction into contact with high-temperature products undergoing reaction in the reforming zone or in the high-temperature cracking zone and effecting a short-time cracking of the heavy fraction. In other Words, heavy fractions from the viscosity-breaking operation which are not well adapted for ordinary drastic cracking operations may, in accordance with the invention, be combined with a stream of highly heated cracked or reformed products and subjected to an intensive cracking operation conducive to the formation of high anti-knock gasoline constituents, but under conditions in which the extent of cracking of the residual constituents of the heavy fraction may be appropriately limited, so that over-cracking, which would produce coking difiiculties, may be avoided.

In order to more completely disclose the invention, reference will now be had to the: accompanying drawing, which is a flow diagram illustrating apparatus adapted for the practice of the invention.

The drawing shows a cracking coil 1 and a reforming coil ll installed in suitable furnaces and communicating with a reaction chamber l2 provided with fractionating towers l3 and I4, and abranch 22 leading to the viscosity-breaking coil [5. A line 23 is provided for conducting bottoms from the dephlegmator l3 to line 22 for introduction to the viscosity-breaking coil [5.

As stated, the viscosity-breaking coil l discharges into the evaporator IS. The evaporator is shown provided with a fractionating section 24 and a trap-out tray 25 for removing a heavy out. A vapor line 26 extends to the fractionating tower H. A condenser coil 21 serves for condensing the overhead vapors from the tower II, the condensate being collected in receiving drum 28. Reflux condensate from the tower I1 is drawn through line 29 and directed by pump 30 through line 3! to the high-temperature cracking coil Ill. Reflux condensate from tower I4 is drawn through line 32 and directed by pump 33 through line34 to the cracking coil Ill. The charge to the cracking coil Ill may thus comprise reflux condensate from either or both of the towers l4 and II.

The products from the cracking coil I!) pass through a transfer line 35 to the enlarged reaction chamber l2. The residue separated out from the viscosity-broken products in evaporator l6 may constitute the heavy fraction which is brought into contact with the highly heated products discharging from the cracking coil ID for short-time reaction therewith, and for the purpose of carrying out such operation, a line 36 leads from the evaporator 16 to a pump 31 which forces the residue through line 38 to transfer line 35 for introducing the heavy stock into the reaction chamber I2. Instead of using the residue from the evaporator l6 as the heavy fraction to be introduced into the cracking chamber l2, or in addition to this residue, the heavy condensate collected in trap-out tray 25 may be so employed. For this purpose, a line 39 leads from the trap-out tray 25 to a pump 40 by which the heavy condensate may be pumped through line 4| to line 38 for introduction to the transfer line 35. In cases where it is not desired to introduce this condensate into the reaction chamber [2, the condensate may, in accordance with the invention, be cycled to the viscosity-breaking coil l5, as through the branch lines 42. Thus in accordance with the invention, either the heavy residue or a heavyor viscous gas oil cut, or both such residue and heavy gas oil, which materials are not suited for ordinary high-temperature, high cracking per pass operations, may be directed to the transfer line 35 to be subjected to intensive cracking conditions, due to the contacting with the products from the high-temperature cracking coil.

As indicated in the drawing, the transfer line 35 preferably enters the reaction chamber l2 at the upper end thereof, so as to thus provide for down-flow in the reaction chamber. A vapor line 43 is shown for conducting separated vapors from the cracking chamber I2 to the primary fractionating tower l3, and a tar or residue line 44 is indicated for withdrawing tar or residue from the cracking chamber. In practicing the invention, residual material is not permitted to accumulate in the reaction chamber l2, the tar or residue being withdrawn at such a rate as to effectively prevent the accumulation of liquid therein. Thus, in accordance with the invention, the heavy stock from the viscosity-breaking operation is brought into intimate contact with the high-temperature products from the cracking coil ID, to thus subject the heavy stock to intensive cracking conditions conducive to the formation of constituents of high anti-knock quality, and due to the rapid separation of liquid constituents from vapors in the reaction chamber l2, and by reason of the fact that the liquid constituents are not permitted to accumulate therein, the over-cracking of residual constituents into coke is largely prevented. In this way heavy stocks from the viscosity-breaking operation, which are not well adapted for ordinary hightemperature cracking, may be utilized to produce an additional yield-of gasoline without any material sacrifice of anti-knock quality in the ultimate product.

The vapors which pass through vapor line 43 are subjected to fractionation in the primary and secondary towers l3 and M. The heavy condensate separated out in tower l3 or, in the event that charging stock is introduced into this tower, the composite fraction of reflux condensate and unvaporized constituents of the charging stock, is withdrawn through line 23 for introduction to the viscosity-breaking coil 15, and the secondary condensate, which is well adapted for high-temperature, high cracking per pass cracking, is cycled to the high-temperature crackingcoil I0. The overhead vapors from the tower M are condensed in condenser coil 45, the distillate being collected in receiving drum or gas separator 46. The distillate thus collected in receiving drum 4% constitutes a gasoline stock of high anti-knock value.

The fractionation of the vapors evolved in the evaporator I6 and tower I1 is advantageously carried out in such a way as to separate out a heavy condensate in the trap-out tray 25, an intermediate condensate in the bottom of the tower I1, and a light distillate collected in the receiving drum 28. Thus the fractionation may be so conducted as to segregate in the trap-out tray a highly viscous condensate or a stock containing a very high percentage of waxy constituents. The stock thus segregated in the trap-out tray 25 may be either cycled to the viscosity-breaking coil for further cracking under viscosity-breaking conditions or directed through line 4| to the transfer line 35 to be thus subjected to an intensive cracking conducive to the formation of superior anti-knock quality gasoline constituents.

The fractionation of the vapors remaining uncondensed after the segregation of the heavy gas oil out may be so conducted as to separate out a light stock adapted for vapor-phase cracking or to segregate a particular gasoline fraction which it is desired to subject to reforming. Thus the fractionation may be so conducted as to separate out a fraction collected at the bottom of the tower I! which will include the gasoline constituents which it is desired to reform. This cut may be designated as a heavy naphtha or light gas oil out, and will contain a large proportion of constituents in the gasoline boiling range. The initial boiling point of this cut will generally be from about 200 to 300 F. The overhead vapors from the tower ll may be subjected to condensation in the coil 27 and collected as a light gasoline distillate in the receiving drum 28. In case it is desired to subject to reforming the entire gasoline cut, it is unnecessary to fractionate the gasoline into a light and heavy out.

In accordance with a modification of the invention the vapors evolved in the evaporation of the viscosity-broken products may with advantage be fractionated to segregate a light gas oil out adapted for vapor-phase cracking and a gasoline cut to be reformed. In carrying out this type of operation, a separate reforming coil H is provided and thus a light gas oil stock adapted for vapor-phase cracking for conversion into lower boiling or gasoline constituents may be withdrawn from tower ll through line 29 and directed to the high-temperature cracking coil l6, and, as shown in the drawing, the fractionating tower I! may be provided with a trap-out tray 41 with a line 48, pump 49, and line 56 for introducing the desired gasoline cut to the reforming coil II. A branch line 5! is indicated for withdrawing distillate from the receiving drum 28, in the event it is desired to subject to reforming the distillate collected in receiving drum 28. Thus, in accordance with the invention, a light gas oil cut adapted for high cracking per pass or more particularly for vapor phase cracking for conversion into gasoline may be withdrawn from the tower 11 through line 29 and directed by pump 30 through line 31 to the high-temperature cracking coil Ill, while a gasoline stock introduced by the pump 49 to the reforming coil I I is subjected to reforming conditions to increase its anti-knock quality.

In one modification contemplated by the invention the gasoline stock to be reformed is collected in the bottom of the fractionating tower H, with or without the addition of some higherboiling constituents, and this gasoline-containing stock is directed by pump 30 through line 3! and a branch line 52 to line 50 and thence to the reforming coil H, while the stock directed to the high-temperature cracking coil it! may consist of the cycle condensate withdrawn from tower l4 and introduced by pump 33.

In practicing the invention, the charging stock or commingled charging stock and reflux condensate from the tower l3 may be subjected to moderate conditions of cracking in thecoil 15 adapted for effecting a reduction in the viscosity of the oil and for producing a relatively large yield of constituents suitable for further conversion into gasoline and a relatively smaller yield of gasoline. The best temperature conditions for this operation involve temperatures of about 850-880 F. under conditions of a cracking per pass of about 815%, usually about 10-12%. Practical operating pressures are about 200-400 lbs. The pressure may with advantage be reduced in the evaporator I6 to low super-atmos pheric pressures or to pressures approximating atmospheric.

The temperature in the reforming coil I I should not be under 850 F., and to obtain best results should exceed 900 F., in order to accomplish the desired rearrangement of the hydrocarbon molecules in the gasoline to effect a conversion into hydrocarbons of increased anti-knock quality.

The temperatures employed in the cracking coil Ill may include any suitable temperature conditions adapted for sustaining high rates of cracking per pass, such as a cracking per pass of 20% and higher, so that the conversion therein will be under conditions in which gasoline of high antiknock character is formed. Temperatures of the order of 900 F. or 1000 F. may be recommended, although higher temperatures adapted for intensive cracking under relatively short time conditions may be employed with advantage. In the event that the cracking coil I is also used for reforming gasoline constituents introduced thereto, the temperatures employed should be within a range adapted for accomplishing reforming.

It is an object of the invention to maintain cracking temperatures in the reaction chamber I2 of the commingled products introduced thereto, including the heavy fraction from the viscositybreaking operation, sufficiently high to maintain conditions of conversion therein capable of sustaining a rate of cracking per pass adapted to produce high anti-knock gasoline. A temperature of 850 F. is approximately the minimum temperature adapted for this purpose. At the same time the temperature must not exceed a range adapted for sustaining a condition of liquidity adjacent the point at which residual constituents are withdrawn from the chamber. It may be pointed out that within certain temperature ranges the heavy stock introduced into the reaction chamber I2 into contact with the highly heated products from either or both of the high temperature cracking coils I0 and I2 actually serves to prevent coking under conditions where liquid is withdrawn at a rate adequate to prevent the accumulation of liquid in the chamber. The upper limit of this temperature range is approximately 930 F. Thus the temperatures maintained in the reaction chamber I2 should exceed 850 F. in order to maintain conversion conditions therein adapted for the production of anti-knock gasoline, but should not exceed about 930 F. While the pressures employed may vary considerably and still facilitate an efficient operation, pressures of about 200 lbs. to 400 lbs. are to be recommended for the reaction chamber I2.

In one modification contemplated by the invention, the gasoline constituents from the viscositybreaking operation, which it is desired to reform, may be directed by pump 49 through line 50, or by pump 30 through lines 3| and 52 thence into line 50, and passed through line 53 to the transfer line 35 for introduction into the reaction chamber I2. In this way the gasoline constituents to be reformed are brought into contact with the highly heated products from the cracking coil III, as well as in contact with the heavy or residual stock from the viscosity-breaking operation introduced through line 38 and the reformation of the gasoline constituents is accomplished in the transfer line 35 and reaction chamber I2 wherein reforming conditions are maintained.

The residue withdrawn from the reaction chamber I2 through line 44 may be withdrawn to storage or to a tar flashing unit. In one method of operation contemplated by the invention the residue withdrawn through the line 54 may be introduced to the evaporator I6, so that this residue may be subjected to distillation, together with the products from the viscosity-breaking coil I5. The resultant residue formed in the evaporator I6 consisting of the viscosity breaker tar and cracked tar from the cracking chamber I2 may be Withdrawn from the evaporator I6 to constitute a residual product of the process. If desired, a portion of such residue may be cycled through line 36, pump 31, and line 38 to the reaction chamber I2, to thus subject such portion to a further intensive cracking, but of limited duration, due to the prevention of liquid constituents in the reaction chamber I2.

In one method of operation contemplated by the invention, the heavy oil from the viscosity breaking operation, instead of being introduced into the transfer line from the cracking and reforming coils or into the reaction chamber, may be introduced into the latter portion of either the reforming coil or the cracking coil, or a portion of such heavy oil may be introduced into the latter section of the cracking coil and another portion of the heavy oil introduced into a latter portion of the reforming coil, the commingled products passing thence through the transfer line into the reaction chamber. In another modification contemplated by the invention, the highly heated products from the cracking coil or from both the cracking coil and reforming coil may, before being introduced into the reaction chamber IZ, be passed into a soaking or reaction zone, preferably in the form of a coil insulated or moderately heated to prevent loss of heat, and the heavy stock from the viscosity breaking operation passing through the line 38 may also be introduced into this soaking section. In this way the heavy stock may be subjected to a further extent of cracking than when introduced directly into the transfer line 35 or into the reaction chamber I2. 'I'he cracking and reforming reactions may be continued on the commingled products upon being introduced into the reaction chamber I2, but by preventing the accumulation of liquid therein the undue cracking of liquid or residual constituents is prevented. In this method of operation both the soaking zone and the reaction chamber should be maintained at a cracking temperature adequate to sustain reactions yielding products of high anti-knock quality.

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 such limitations should be imposed as are indicated in the appended claims.

What I claim is:

1. The process of cracking hydrocarbons that comprises passing hydrocarbon oil through a cracking coil to subject the oil to cracking therein, directing resultant cracked products into a reaction chamber maintained at a cracking temperature in which separation of vapors from liquid occurs and from which liquid is withdrawn at a rate adequate to prevent the accumulation of liquid therein, passing separated vapors to a primary fractionating zone, introducing charging stock comprising residual constituents of crude petroleum into contact with vapors therein and forming a composite fraction therein separate from said liquid being withdrawn from the reaction chamber and comprising resultant reflux condensate and unvaporized constituents of the charging stock, passing uncondensed vapors to a secondary fractionating zone wherein fractionation is carried on to separate out a gasoline distillate and a reflux condensate, directing reflux condensate thus obtained to said cracking coil, passing said composite fraction from the primary fractionating zone through a heating coil and subjecting the oil therein to moderate cracking conditions adapted to produce viscosity breaking thereof, fractionating the viscosity-broken products in a separate fractionating zone to separate out a heavy fraction and a light gasoline-containing fraction, directing the light gasoline-containing fraction to said cracking coil, maintaining temperature conditions in said cracking coil adequate to effect reforming of gasoline constituents, and bringing said heavy fraction into contact with cracked products discharged from said cracking coil to effect the cracking thereof in said reaction chamber.

2. The process of cracking hydrocarbons that comprises passing hydrocarbon oil through a cracking coil to subject the oil to cracking therein, directing resultant cracked products into a reaction chamber maintained at a cracking temperature in which separation of vapors from liquid occurs and from which liquid is withdrawn at a rate adequate to prevent the accumulation of liquid therein, passing separated vapors to a primary fractionating zone, introducing charging stock comprising residual constituents of crude petroleum into contact with vapors therein and forming a composite fraction therein separate from said liquid being withdrawn from the reaction chamber and comprising resultant reflux condensate and unvaporized constituents of the charging stock, passing uncondensed vapors to a secondary fractionating zone wherein fractionation is carried on to separate out a gasoline distillate and a reflux condensate, directing reflux condensate thus obtained to said cracking coil, passing said composite fraction from the primary fractionating zone through a heating coil and subjecting the oil therein to moderate cracking conditions to produce viscosity breaking thereof, fractionating the viscosity-broken products in a separate fractionating zone to separate out a heavy fraction and a light gasolinemontaining fraction, subjecting said light gasoline fraction to conditions of temperature to effect the reforming thereof into constituents of increased antiknock quality, directing the products of such reforming into aforesaid reaction chamber, and introducing said heavy fraction into said reaction chamber to be contacted therein with the products of said reforming and the products discharged from said cracking coil.

3. The process of cracking hydrocarbons that comprises heating hydrocarbon oil in a continuous flowing stream to cracking temperature to effect cracking, directing the stream of cracked products into a vapor separating chamber wherein separation of vapors from residue takes place, passing the separated vapors to a primary fractionating zone, introducing charging stock comprising residual constituents of crude petroleum into the primary fractionating zone to dephlegmate vapors therein and forming a composite fraction therein comprising unvaporized constituents of the charging stock and heavy reflux condensate, passing uncondensed vapors from the primary fractionating zone to a secondary fractionatingzone wherein fractionation is carried on to separate out a gasoline distillate and a reflux condensate, directing reflux condensate thus obtained from the secondary fractionating zone to aforesaid continuous flowing stream of hydrocarbon oil undergoing cracking, passing said composite fraction from the primary fractionating zone to a viscosity-breaking zone wherein the composite fraction is heated at a cracking temperature and subjected to cracking conditions to effect viscosity breaking, fraotionating resultant viscosity-broken products in a separate fractionating zone to separate out a heavy fraction and a light fraction comprising gasoline constituents, heating said light fraction containing gasoline constituents in a continuous flowing stream to a cracking temperature adequate to efiect reformation of gasoline constituents, introducing said heavy fraction into said flowing stream of gasoline constituents undergoing reforming, at a point therein after such cracking temperature is attained, to thereby subject said heavy fraction to cracking temperature to effect conversion into lower boiling products, separating the resultant commingled cracked products into vapors and residue and passing the separated vapors to said primary fractionating zone.

4. The process of cracking hydrocarbons that comprises passing hydrocarbon oil through a cracking coil to subject the oil to cracking therein, directing resultant cracked products into a reaction chamber maintained at a cracking temperature in which separation of vapors from liquid occurs and from which liquid is withdrawn at a rate adequate to prevent the accumulation of liquid therein, passing separated vapors to a primary fractionating zone wherein the vapors are subjected to fractionation to form a heavy reflux condensate, passing uncondensed vapors from the primary fractionating zone to a secondary fractionating zone wherein fractionation is carried on to separate out a gasoline distillate and reflux condensate, directing reflux condensate thus obtained from the secondary fractionating zone to said cracking coil, combining charging stock comprising residual constituents of crude petroleurn with heavy reflux condensate formed in the primary fractionating zone and directing the constituents thus combined to a viscosity-breaking zone wherein said constituents are heated at a cracking temperature and subjected to cracking conditions to effect viscosity breaking, fractionating resultant viscosity-broken products in a sepa rate fractionating zone to separate out a heavy fraction and a light fraction containing gasoline constituents, subjecting said light fraction containing gasoline constituents to conditions of temperature to effect reforming thereof into constituents of increased anti-knock quality, directing the products of such reforming into aforesaid reaction chamber, and introducing said heavy fraction into said reaction chamber to be contacted therein with the products of said reforming and the products discharged from said cracking coil.

WAYNE E. KUHN.

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