US1819542A - Process for converting petroleum hydrocarbons - Google Patents

Description

Aug. 18, 1931. R. CROSS 1,819,542

PROCESS FOR CONVERTING PETROLEUM HYDROCARBONS Filed March 1926 LE INVENTOR.

i qy 6 /2146 A TTORNE Y.

Patented Aug. 18, 1931 UNITED STATES PATENT OFFICE ROY CROSS, OF KANSAS CITY, MISSOURI,

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

GASOLINE PRODUCTS GOMPAN Y, INC., OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE PROCESS FOR CONVERTING PETROLEUM HYDROCARIBONS Application filed March 17, 1926. Serial No. 95,269.

This invention relates to improvements in a process and apparatus for converting petroleum hydrocarbons, and relates more particularly to a process in which the reflux condensate or higher boiling point fractions uncontaminated with free carbonaceous matter and relatively none of the heavy polymers which are separated from the oil during cracking or distillation is returned to an m advanced stage of the heating zone and thereafter subjected to further cracking or conversion.

Among the important objects of the invention are to provide a process in which the oil is raised to a cracking temperature in the heating zone and thereafter accumulated and the conversion substantially completed in an enlarged reaction or cracking stage, wherein the oil is maintained under tempera ture and pressure conditions regulated to prevent any substantial distillation; to provide a process in which the oil on discharge from the reaction stage has the pressure thereon reduced, whereby the lighter fractions are separated in the form of vapors due to the reduction of pressure and the contained heat in the oil; to provide a process in which these lighter fractions are subjected to a dephlegmating action, the heavier or higher boiling point fractions being separated out in the form of reflux condensate and returned to an advanced portion of the heating stage, or that portion wherein the higher temperatures are present in order to produce further conversion in the relatively refractory refluxed materials; to provide a process in which the lighter fractions passing overhead from the dephlegmating or reflux condenser are subjected to a final condensing action and collected as an ultimate distillate, and in general to provide a process and apparatus of the character hereinafter described in more detail.

The single figure is a diagrammatic side elevational View of the apparatus with parts in section and parts broken away.

Referring to the drawing. At 1 is shown a furnace in which is mounted a heating coil, the lower portion of the coil being 59 designated as 2, while the upper, or advanced stage of the heating coil or the tubes arranged around the rear and upper part of the ceiling of the furnace designated as 3. At 4 is shown a reaction chamber which is heavily insulated to prevent loss of heat by radiation, andis preferably fabricated by vforging a single ingot of steel into an enlarged chamber having bottled necked ends, which are flanged to accommodate the removable end plates which facilitate the cleaning of the furnace. An evaporator 5 1s connected to the reaction chamber by means of a transfer line 6 controlled by the reduction valve 7. A vapor line 8 connectrng into the top of the vaporizer communicates with the dephlegmator or refluxing tower 9, which is preferably of the hubble type, in which the vapors rise through a series of pools of oil, the condensates bemg separated out and gravitating downwardly through the pools in the tower in an opposed direction tothe flow of the vapors. A vapor line 10 leads from the top of the tower to 'a condenser coil 11, positioned in the water cooled condenser box 12. The discharge end of the coil 11 terminates in a pipe 13 which is connected to the gas separator 14:. The gas separator has a liquid draw-off line 15, controlled by a valve 16 and a gas draw-off line 17 regulated by a valve 18. Heavy residual oil accumulating in the evaporator 5 is drawn off through the pipe 19 controlled by a valve 20 automatically regulated by a liquid level control device designated as 21. The pipe 19 leads to a cooling coil 22 positioned in the water cooling box 23; the discharge from the coil is directed through pipe 24 to storage, not shown. The reflux condensate separated out in the tower 9 is drawn off through the line 25 controlled by valve 26, which is manipulated by the liquid level control device 27. An accumulating tank may be interposed in the line 25 in order to furnish a constant supply of oil to the hot oil pump '28, which serves to return the reflux to an advanced stage of the heating, coil or to the tubes which are subjected to the higher ternperature of the furnace.

In operation charging stock is supplied from any convenient source, not shown, through the pipe 29 and is circulated by means of the pump 30 through the line 31, thence through the heat exchanger coil 32, positioned in the top of the refluxing tower 9 where the circulation of the cool charging stock in a closed coil serves not only to preheat the incoming oil, but to assist in the dephlegmation of the vapors in the tower. From the heat exchanger coil 32 the oil is directed through the line 33 and introduced into the lower portion of the bank of tubes designated as 2. These tubes are connected to form a continuous coil the oil passing from the cooler part of the furnace upwardly through the tubes to the hotter portion of the furnace. Near the upper portion of the bafiie Wall, designated .as 34 in the drawing, the heating tubes instead of being arranged centrally in the tube compartment of the furnace, are positioned along the back and side walls, and upon the ceiling of the furnace, thus taking advantage of the radiant heat which produces a more economical and effective heat exchange between the combustion gases and the medium to be heated. The oil passes successively through these separate tubes and is discharged through the transfer line 35 into the reaction chamber 4. The velocity of the oil and the temperature of the furnace is so regulated that the oil in its passage through the furnace is raised to a cracking temperature substantially as it approaches the transfer line, in order that there shall not be any considerable cracking or vaporization which produces deposition and accumulation of free carbonaceous material in the tubes.

On being discharged into the reaction chamber the oil is retained therein for a suflicient period of time to complete the cracking which was initiated in the heating tube. In the reaction chamb r the carbonaceous matter settles out and the cracked products are discharged to the transfer line 6 through the reduction valve 7 into vaporizer 5. As described, this reduction of pressure and the high temperature of the cracked products produces an evolution of the lower boiling point fractions and under certain conditions and with certain types of oils, it is necessary to introduce 'a. cooling hydrocarbon medium, or steam into the transfer line 6 just subsequent to the reduction valve or into the bottom of the vaporizer to retard excessive vaporization, as certain oils tend to completely vaporize to coke unless some such provision is made.

In any event the conditions being properly controlled a satisfactory fuel oil bottom is recovered and drawn off through the line 19, and after cooling isdirected to storage through the line 24. The overhead material passing through the line 8 is directed to the tower 9 where it is subjected to dephlegmation as described.

The temperature at the top of the tower 9 is controlled to permit those hydrocarbon fract ons to and including the end boiling point f commercial gasoline to pass overhead and to make up the final distillate re- .covered after condensation in the gas separator 14. The uncondcnsable gas may be drawn off through the line 17 and reused in the system as fuel, or in separate apparatus at the operators convenience.

Returning now to the particular novelty of the invention and that portion of the process which is different than the normal practice hereinhefore described, the reflux condensate drawn off from the bottom of the tower, instead of being returned to the inlet' of the heating coil, is recharged to an advanced stage of the heating coil. The particular point of introduction of this returned condensate can be best ascertained by the individual characteristics of the furnace and the temperatures existing therein.

It is advisable to return the condensate at a point Where it will arrive and be introduced into the charging stock passing through the heating coils substantially at the temperature of the charging stock at the point it is introduced or slighly above that temperature.

By returning the condensate in this manner the efficiency of operation may be maintained, eliminating the necessity of cooling down this relative refractory oil by charging it directly into the inlet stream and subsequently reheating the recycled condensate when intermingled with the charging stock to temperatures at Which it will be converted or cracked. By recycling the con- I densate in this manner a considerably greater yield of ultimate distillate may be had from the combined oils and the formation and deposition of carbonaceous material in the coil substantially eliminated. Furthermore it is found that a considerably better heat exchange is effected and somewhat lowe'r temperatures may be used in the furnace when operating on the same oils when this type of operation is contrasted with the return of the reflux to the inlet end of the heating tube. It will be appreciated that by injecting oil, from an extraneous source, into the heating tubes of uniform cross section a material increase of velocity is obtained. This is decidedly advantageous in a cracking process inasmuch as the increase in velocity tends to sweep along and carry in suspension any carbonaceous material which might be formed in the hotter portions of the tube. It is recognized that it is a known practice to return the bottoms from' the vaporizer to an advanced stage of the. heating coil for retreatment, but this practice is objectionable as residual oil, such as recovered from that portion of the system, contains considerable free carbonaceous mat ter, which rapidly accumulates and clogs the pipes of the heater, rapidly hindering the operation and reducing the capacity of the plant to the extent that it must be shut down frequently for cleaning the tubes.

As described an accumulative tank may be interposed in the line 25 in order to main tain a relative constant supply of oil for the circulating pump 28.

I claim as my invention:

1. A process for converting petroleum hydrocarbons, comprising the steps of raising the oil to a cracking temperature in a two stage heating coil, positioned in a heater, effecting the cracking thereof in a reaction stage, subjecting the vapors evolved from the cracked product to a reflux condensing action out of contact'with fresh feed, condensing the vapor passing overhead from the refluxing stage to produce an ultimate distillate, and recycling the refluxed condensate directly to the stage of the heating coil receiving the greater heat and blending it with oil for treatment, which is of a different character within said stage of the heating coil receiving the greater heat.

2. A process for converting petroleum hydrocarbons, comprising the steps of raising the oil to a cracking temperature in a twostage heating coil, effecting the cracking thereof in a reaction stage, subjecting the vapors evolved from the cracked products to a reflux condensing action out of contact with fresh feed, condensing the vapors passing overhead from the dephlegmating stage to produce an ultimate distillate, and recycling the refluxed condensate and injecting it into that part of the heating coil subjected to the most intense heat whereby the velocity of the oil in said increased.

3. A process for converting petroleum hydrocarbons, comprising the steps of raising the oil to a cracking temperature in a heating coil, effectin the cracking thereof in a reaction stage, su jecting the vapors evolved from the cracked products to a refluxed condensing action out of contact with fresh feed, condensing the vapors passing overhead from the dephlegmating stage to produce an ultimate distillate, and recycling the refluxed condensate to an advanced'stage of the heating coil subjected to the most intense heat and blending it therein with the charging stock which has been raised to substantially a temperature of the refluxed condensate. I

4. A process such as that described in claim 2, in which the reflux condensate is returned to an advanced stage of the heating coil under mechanically applied pressure,

5. A process for converting petroleum hypart is appreciably v heat section to be directly blended with the oil passing through the furnace.

6. A process for converting petroleum hydrocarbons comprising passing a stream of charging stock through a furnace including successively connected convection and radiant heat sections, to raise the oil to cracking temperatures while maintaining high pressures thereon, passing the oil thence to an enlarged chamber, then reducing the pres sure upon the oil and passing it to an evaporating stage wherein the lighter fractions are distilled ofl", refluxing the lighter fractions and accumulating a clean hot reflux condensate, and passing the hot condensate directly to the radiant heat section of the heating stage.

ROY CROSS.

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