US2039763A - Method of coking liquid hydrocarbons - Google Patents

Description

May 5, 1936.

C. W. ANDR'EWS ET ALl METHOD OF COKING LIQUI) HYDROCARBONS Filed July 5, 1932 Charles RO dndrews- 5- Petersen.

Patented May' 5*, 193e UNITED STATES PATENT OFFICE IVIETHOD 0F COKING LIQUID HYDROCARBONS Charles W. Andrews, Chicago, Ill., and Roy S.

Petersen, San Antonio, Tex., assignors to Brassert Tidewater Development Corporation,

1 Claim.

This invention relates to a new and improved method of treating hydrocarbons and more particularly to the coking of residues of petroleum hydrocarbons,

In other methods of coking residues from cracking processes the residue is preheated to temperatures about 800 F. or as much higher as possible without coking up the preheater tubes. Considerable difficulty is being experienced by this practice, the runs are short, and the down time for clean outs increases with the increase in temperatures. It is desirable to get the charge to the coke oven at as high a temperature as possible, bringing about complete vaporization, and depositing the heavy bottoms on the iloor where the external heat removes volatile matter present.

In our new and improved method the residuum is drawn hot to the coke oven and additional heat applied by the admittance of hot oil direct from the transfer line of the cracking process. In this manner we have eliminated thenecessity of preheating the residuum and avoid entirely the difculties experienced by these other methods.

The assistance in coking charging stocks by means of the heat carried into the oven by hot oil from the transfer line is of great importance as many residua will be found which cannot be satisfactorily preheated to high enough temperatures to permit rapid coking and cracking in the oven. By our method we not only have theheat supplied through the floor of the oven, but also this additional heat through the material from the transfer line.l

By our method we propose to take the heavy residues or oils direct from the reaction or expansion chamber of the cracking unit while still hot, and charge `the residue into a coking oven or in proximity to the oven in a chamber which may be superposed thereupon and in direct connection therewith.

The purpose of this method is to allow the heavy residue which is formed in the cracking process to be deposited in a coking chamber in such a way that the released pressure permits instant vaporization of a large percentage of the residue. Hot oil is to be passed direct from the transfer line of the cracking unit at temperatures above 800 F. either into the chamber connected to the coking chamber, orvdirectly into the coking chamber, or it may be passed to both chambers. Further vaporization. of residue, due to increase in temperature, is brought about. The heavy bottoms from both residue and hot oil lines just admitted, deposit in the coke oven where external heat drives oil all volatile matter and forms a dry coke.

It is an object of the present invention to provide a new and improved method for the treat ment of hydrocarbons and more particularly to 5 the coking of petroleum hydrocarbons.

It is also an object to provide a method capable of being carried out at substantially atmospheric pressures. It is an additional object to provide a method in which the solid residue may be rel0 covered as a hard dense coke of low volatile content. v

It is a further object to assist in coking residues by means of heat carried into the oven by hot oil from the transfer line from the cracking unit l5 operation.

Other and further objects will appear as the description proceeds.

We have shown somewhat diagrammatically in the single gure of the accompanying drawing, 20 an elevational layout with parts in section showing apparatus for carrying out our improved method.

In the drawing, the cracking unit I I, expansion and reaction chamber I2, cracking unit bubble 25 tower I3, condenser Il, and gas separator I5 form part of the usual cracking unit layout and in themselves form no part of the present invention. The present invention comprises the coke oven I6, mixing chamber I1, separator I9, and gas separator 20, together with the various connections between these elements and the elements comprising the usual cracking unit.

The charging stock line 2| having the pump 22 leads to the line 23. This line 23 is connected 35 with the bottom of the cracking unit bubble tower I3 and leads through pump 24 and line 25 to the heating coils 26 in the cracking unit furnace. From the cracking unit furnace coils 26, the line 21 leads to an intermediate point in the expan- 40 sion and reaction chamber I2. A branch 28 of the line 21 controlled by valve 29 leads to the mixing chamber and coke oven. The line 30 leads from the bottom of the expansion and reaction chamber iz to distributing means 3| m the top 45 of the mixing chamber I1.

The overhead line 32 leads from the top o1' the expansion and reaction chamber I2 to an intermediate portion of the cracking unit bubble tower I3. The overhead from tower line 33 to the condenser I4 and through line 3lv to an intermediate point in the gas separator II. From the top of the gas separator I5 the line 35 leads to the line 36 which. leads to the gas absorption plant not shown. 55

I 8, condenser 30- I3 passes through 50 Gasoline draw-off line 31 leads from a point in the gas separator I5 adjacent its lower end. This line 31 is provided with pump 38 and has a branch line 39 leading from a point beyond the pump to the distributing header 40 in the top of the cracking unit bubble tower I3.

The line 4I leads from the top of the mixing chamber I1 to ,the lower part of the separator I8. The line 42 leads from an intermediate portion of the separator I8 through pump 43 and line 44 to the expansion and reaction chamber I2.

Separator I8 is provided with the drain 45 controlled by valve 46. 'I'he overhead line 41 leads from the top of the separator I6 and condenser I9 from which the line 48 leads to the gas separator 20.

The line 49 leads from the lower portion of the gas separator through pump 50 and line 5I to the upper portion of the cracking unit bubble tower I3. The gas draw-off line 52 leads from the top of the gas separator 20 to the line 36 leading to the gas absorption plant. The line 53 leads from the gas absorption plant and is provided with branches 54 and 55 leading to the-combustion space under the coke oven I 6, and with the branch 56 leading to the cracking unit furnace. The coke oven I 6 may be provided with mechanical coke pusher 51 and with car 58 located at the opposite side of the ovens to receive the coke pushed from the oven by the pusher.

The bubble tower I3 of the cracking unit may be used to fractionate the overhead from the reaction chamber of the cracking unit and is shown as provided with the distillate draw-olf line 59. It will be understood that a plurality of such lines may be provided at different points in the tower.

'I'he line 28 branches to form line 6I, controlled by valve 62, leading to the mixing chamber, and line 63 controlled by valve 64 leading to the coke oven. 'I'he connectionV of line 63 to the coking chamber is preferably spaced from the connection between the coke oven and mixing chamber so as to permit transfer of heat from the volatile portion discharged from line 63 before this portion leaves the oven chamber.

The apparatus on the upper line of the single lgure of the drawing is an oil cracking unit layout of a character now in somewhat general use. In operation of this unit the charging stock is mixed with the condensate from the bottom of the cracking unit bubble tower I3 and the mixture passed through the cracking unit furnace I I. From this furnace the highly heated hydrocarbon material in liquid form, which isusually heated to a temperature in excess of 900 F., when a coking operation is preferred, is discharged into the expansion, reaction or flash chamber I2. The chamber I2 indicates the chamber in which the residue is finally collected before leaving the cracking unit. 'I'he showing of this chamber in the drawing is diagrammatic in character and is intended to indicate any form of apparatus in which vaporization occurs under cracking conditions and a heavy liquid hydrocarbon residue is formed and is customarily removed from the process. 'I'he term reaction chamber in the claim is intended to cover any such apparatus. 'I'his chamber is normally operated under considerable Y pressure which may approximate pounds per square inch. The overhead distillate from this reaction chamber I2 passes to the cracking unit bubble tower I3 where it is cleaned and fractionated and the overhead from this tower passes through condenser I4 and to the gas separator I5. The gasoline is drawn oi from the lower portion of the separator and the flxed gas drawn from the top of the separator.

It will be understood that any sized distillate fractions may be drawn oil at different points in the bubble tower. In normal operation of apparatus of this character the condensate from the bubble tower may be four or ve times greater than the amount of new charging stock mixed with it before passage through the furnace. This stock is therefore continually recycled until the original charging stock is broken down to coke in'the expansion and reaction chamber and light distillates and fixed gas drawn oi from the bubble tower and gas separator. The continued recycling and the discharge of the liquid into the reaction chamber while at a high temperature causes the reaction chamber to gradually iill with coke which ultimately must be withdrawn from the chamber by stopping the process.

In some methods of carrying out the process the residue from the reaction chamber is drawn off as a heavy hydrocarbon liquid at the reaction temperatures, but which may be solid under ordinary atmospheric conditions. In other methods of operation the residue is liquid at normal temperatures. These residues contain material quantities of volatiles including gasoline and have no commercial use so that it is more customary to carry the reaction to reduce the residue to coke in the reaction chamber.

The processes outlined above are already in use and do not in themselves constitute the present invention. According to the present invention the process as outlined above is carried on with modications which add to the eiliciency of the process in giving increased yields of gasoline and lighter distillates and in producing a harder, denser coke with a smaller percentage of volatiles than is possible in usual reaction chambers. An additional feature is that the coke may be readily removed from the oven in which it is formed at a very low cost and without material delav in the process. This is contrary to the removal of coke from the usual type of pressure reaction chamber, which is expensive and occasions considerable delay in the operation of the apparatus. It isroften considered good practice if the coke can be removed for the price received for it in cleaning these reaction chambers, while it is possible to remove the coke from applicants chamber at a cost of a small fraction of the sale value of the coke.

In carrying out the process according to our invention the residue of the expansion and reaction chamber is withdrawn continuously and' passed to the mixing chamber I1. This liquid residue together with the entrained coke or carbon is discharged through nozzles or other contact or spray means in the top of the mixing chamber. It will be understod that this residue will normally be at a temperature approximating '750 F. A portion of the heated mixture of charging stock and bubble tower condensate is drawn off from the line 21 through line 28 controlled by valve 29. This material will be heated normally in excess of 800 or 900 F.. and 1S diS- charged through line 6I controlled by valve 62 into the lower portion of the mixing chamber I1. y

mixing chamber there is substantial vaporization and the volatile portions 'rise and pass in contact with the incoming residue and pass ofl. through line 4I to the separator I8. The heavier particles or coke particles of the heated mixture drop into the coke oven or are entrained by the liquid residue iiowng down through the mixing chamber and carried to the coke oven. The heat derived from this highly heated mixture is a material factor in raising the residue to a temperature approximating that required to coke it.

As an alternative method of operation the heated mixture of charging stock and bubble tower condensate may be passed through line 63 controlled by valve 64 directly into the coke oven. Here the solids will be deposited and the volatiles pass off through the mixing chamber. The heat carried by the material will thus be directly carried into the oven and assist in coking of the mixture of the residue from this material and the residue introduced from the bottom of the reaction chamber. Portions of the material may also be introduced through chamber I1 while other portions go direct to the oven if desired. As a further alternative method of operation, the valve 65 may be closed and the valve 6l opened, allowing the residue to ilow through 6B to 'line 28 and thence into the oven. In this case the mixing chamber I1 may be eliminated.

In our preferred method of operation the overhead materials from the coke oven and mixing chamber are separated in separator I8 and the heavier condensate is forced by pump 43 through line 44 back into the expansion and reaction chamber I2 of the cracking unit. The overhead from the separator I8 is passed through condenser I 9 and to the gas separator 20. It will be understood that the entrained solids and heavier residue from the separator will be periodically drawn oi through line controlled by valve Ii.

As shown in the drawing, the gasoline fromthe gas separator 20 may be returned through line 5I by pump 50 to an upper portion of the cracking unit bubble tower I3. It will be seen, therefore, that our method may be utilized in connection with customary types of cracking units by the addition of a coke oven and a mixing chamber or its equivalent and additional separating and condensing means. It will be understood that the drawing is diagrammatic and that the mixing chamber may vary in size and construction and it is not necessarily located immediately above the coke oven. as materials may be passed from the mixing chamber to the coke oven by means of pumps rather than by gravity.

The coke oven and the mixing chamber will normally be operated at substantially atmospheric pressure. It will be understood, however, that the Amixing chamber may be under a moderate vacuum created in the lines in orde'r to draw the volatiles from the coke oven and through the contact elements of the mixing chamber.

The various elements shown and described may be supplied singly or in batteries of any desired number. For example a plurality of coking ovens may be used with a single cracking unit so that while one oven is being cleared of coke, other ovens may be used to receive the residues being treated.

It will be apparent that this will render the process entirely continuous insofar as the cracking unit is concerned, since no carbon is formed in the expansion, reaction or ilash chambers and consequently there is no need of shut down to clear such chambers.

It will be understood that both the apparatus and method are capable of wide modification to meet varying conditions and requirements and we contemplate such changes and variations as come within the spirit and scope of the appended claim.

We claim:

The method of coking liquid hydrocarbons, which comprises mixing said hydrocarbons with an overhead condensate of the process, passing the mixture through a cracking unit furnace and raising the temperature to a point above 800 F., passing a portion of the heated mixture to a pressure reaction chamber, withdrawing liquid residue from the reaction chamber, mixing with the liquid residue another portion oi' the heated mixture from the cracking unit in a separate mixing chamber whereby the temperature of the residue is raised, discharging this latter heated mixture from the mixing chamber into an externally heated coking chamber maintained at approximately atmospheric pressure, and coking the solid residue of the heated mixture and the reaction chamber residue in the coking chamber to a hard, dense coke.

CHARLES W. ANDREWS. ROY S. PETERSEN.

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