US2895896A

US2895896A - Fluid contact coking in the presence of hydrogen produced by dehydrogenation of product gases

Info

Publication number: US2895896A
Application number: US472460A
Authority: US
Inventors: Ploeg Alfred R Vander
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1954-12-01
Filing date: 1954-12-01
Publication date: 1959-07-21
Anticipated expiration: 1976-07-21

Description

July 21, 1959 A. R. VANDER PLOEG 2,895,896

Nu 1N THE PRESENCE oF HYDROGE FLUID CONTACT COKI PRODUCED BY DEHYDROGENATION OF PRODUCT GASES Filed Deo. 1, 1954 United States Patent O FLUID CONTACT COKING IN THE PRESENCE F HYDROGEN PRODUCED BY DEHYDROGENA- TION OF PRODUCT GASES Alfred R. Vander Ploeg, Port Arthur, Tex., assignor to Texaco Ine., a corporation of Delaware Application December 1, 1954, Serial No. 472,460

2 Claims. (Cl. 208-53) This invention relates to the cracking and coking of hydrocarbon oils by contacting the oil with pulverulent or powdered coke and is concerned with a process in which coke from the hydrocarbon reaction zone is subjected to combustion to provide hot coke for contacting with the oil in the reaction zone.

The invention is directed to a process in which hydrogen is an essential component of the iluidizing gas in the reaction zone and to a method in which hydrogen is produced by contacting recycle gases with highly heated coke from the combustion or burning zone.

In accordance with the invention hydrocarbon oil such as heavy petroleum residual stock is contacted with the coke particles in a reaction zone maintained under fluidized conditions to effect cracking and coking, coke is withdrawn from the reaction zone and is fluidized with air or other oxygen gas to eiect combustion under high temperature conditions so as to produce highly heated coke which is contacted with recycle gases with suicient reaction time to effect conversion to hydrogen and the eiluent products from the hydrogen-forming zone are delivered to the hydrocarbon reaction zone, the formed hydrocarbon constituting an essential uidizing agent in the latter reaction zone.

The production of hydrogen by contacting the recycle gases with the highly heated coke from the combustion or burning zone makes available a relatively cheap source of hydrogen, and the presence of hydrogen in the coking zone is highly beneficial in the coking operation. The hydrogen inhibits coke formation so that less coke is formed with a consequent increase in yield of valuable liquid products such as gas oil. Moreover, the presence of the hydrogen prevents the degradation of the gas oil product which commonly accompanies the ordinary coking operation and produces a gas oil of improved qualities for subsequent catalytic cracking.

For the purpose of more fully explaining the invention reference is now had to the accompanying drawing which is an elevational ow diagram of a preferred embodiment thereof.

In the drawing is a reactor in which the hydrocarbon oil is subjected to fluid contact cracking and coking and 11 is the coke burner or calciner in which coke from the reactor is subjected to combustion. The oil to be subjected to cracking and coking is admitted through a line 12 and one or more branch lines 13 `for discharging the oil into the dense bed of the iluidized mass. Fluidization is maintained in the reactor 10 by means o-f the entry of vapors and gases including hydrogen as is explained hereinafter. The hydrogen-containing gases are relied on as the essential uidizing agent but a small amount of steam may be admitted to the bottom of the reactor for the purpose of stripping hydrocarbons from the coke. The evolved vapors and gases are removed from the dilute phase through a vapor line 14.

Coke is withdrawn from the dense phase of the reactor through a standpipe 15 and is transported in a current of air or other oxygen-containing gas, admitted by a line 16, through a transfer line 17 to the coke burner 11 wherein the coke is subjected to combustion under high temperature fluidized conditions. Flue gases are removed through Vent 18 and the highly heated coke is withdrawn from the burner or calciner 11 through a standpipe 19, a portion of the coke being withdrawn as product coke by a line 20. Due to the high temperature conditions the coke withdrawn from the burner 11 is a low volatile, in fact, a calcined coke.

The highly heated coke from standpipe 19 is picked up by a stream of hydrocarbon gas ilowing in line 21 and the stream of gas with the dispersed coke is subjected to cracking and dehydrogenation to produce hydrogen. This conversion to hydrogen is accomplished by having a suilicient time of reaction in the pipe reactor 21 tol effect substantial production of hydrogen. Alternately, the stream of gases and dispersed coke is diverted from the pipe reactor 21 to a reaction chamber 22 which affords an increased time of reaction. The gases in contact with the highly heated coke are subjected to reaction under lluidized conditions in the uplow reactor 22, the entire products owing through a line 23 and being returned to the transfer line 21 by which the iluidized stream of coke and reaction products including the formed hydrogen is delivered to the reactor 10.

In the fractionating system shown the vapors from the reactor ilowing in lline 14 are delivered to a primary fractionating tower 24, charging stock such as reduced crude or other residual stock is introduced by a line 25 through heat exchanger 26 to the fractionator 24 and the bottom fraction comprising unvaporized charge and reux condensate is withdrawn by a line 27 and directed by pump 28 and line 12 to the reactor 10. The overhead vapors and gases from the tower 24 pass to a secondary fractionator 29 for further fractionation. Gas oil is withdrawn from the latter tower, cooled in exchanger 26 and withdrawn from the system by a line 30 for subsequent use in catalytic cracking or for other purposes. A portion of the gas oil may be directed by pump 31 as reflux in the fractionator 24. The vapors and gases from `fractionator 29 pass through a cooler 32 to a distillate accumulator or receiver 33. The gasoline or naphtha product is withdrawn by a line 34, a portion being recycled by the pump 35 as reflux for the tower 29.

Product gas leaves the accumulator 33 through a line 36. A portion of the gas is conducted by a line 37 and is directed by a compressor 38 through a line 39 to the transfer line 21 for iluidzing and transporting coke received from the standpipe 19 as has been explained. Generally the gas being recycled through line 39 or a portion thereof is passed through a preheating coil 40 before entering the line 21. The gas taken off the accumulator 33 consists predominantly of the normally gaseous hydrocarbons together with some hydrogen. lf desired the gas may be fractionated in order to segregate product hydrogen and so that the recycled gases will consist mainly of light hydrocarbons.

Temperatures in the coke burner or calciner are maintained at a very high level such as 2000-2500 F. in order to supply sufficient heat for the hydrogen forming step. A temperature of 1500 F. is about the minimum temperature that can be used in the coke burner for this purpose and preferably the temperature is maintained substantially above 1500 F. The temperature of the commingled coke and gas in the transfer line reactor 21 and in the reactor 22 is held within a range of about 1200-20007 F. with residence times of 0.120.0 seconds to sustain an effective conversion to hydrogen. The lower temperatures with the longer contact times within these ranges favor the production of aromatics which may be desirable to improve the anti-knock quality of the naptha product. In this way a higher octane naphtha can be produced than in the usual iluid contact coking process while at the same time the cracking qualities of the gas oil product are not impaired due to the presence of the hydrogen in the reactor 10. The gas .recycle rate` is advantageously within a range of about 0.5-10.0 mols per mol of reactor charge. The process is conducted under such superatmospheric pressure as is required to obtain the desired residence time in the hydrogen forming zone and to obtain the beneficial effect of the hydrogen in the uidized coking zone.

The temperature in the cracking and coking reactor is reduced to temperatures that are usual for fluid contact coking operations. Satisfactory temperatures are in the range of about 950 to 1050 F.

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.

I claim:

1. The process of producing a superior gas oil adapted for catalytic cracking that comprises contacting a residual petroleum stock with coke under luidized conditions at cracking and coking temperature in a reaction zone, passing coke from the reaction zone to a burning zone in which the coke is subjected to combustion at a temperature of at least 1500 F., withdrawing coke at a temperature of at least 1500 F. from the burning zone, withdrawing vapors comprising hydrocarbon gas from said reaction zone, dispersing said coke withdrawn from said burning zone in said hydrocarbon gas and passing the dispersion through a dehydrogenation zone at a temperature of about 1200 to 2000" F. for a time of about 0.1 to 20.0 seconds effecting dehydrogenation and formation of hydrogen, delivering eflluent from the dehydrogenation zone comprising coke and hydrogen to the aforesaid reaction zoue to supply heat thereto and maintain iiuidization therein in an atmosphere of hydrogen and fractionating evolved vapors from said reaction zone to separate said gas oil.

2. In the cracking and coking of hydrocarbon oils the process that comprises subjecting hydrocarbon oil to cracking and coking temperature in a reaction zone in contact with coke under iiuidized conditions, withdrawing coke from the reaction zone and subjecting it to combustion in a burning zone at a temperature of at least 1500 F., withdrawing vapors comprising hydrocarbon gas from said reaction zone, withdrawing coke at a ternperature of at least 1500 F. from the burning zone, dispersing said coke withdrawn from said burning zone in said hydrocarbon gas and passing the dispersion at a temperature within the range of about 1200 to 2000 F. through a dehydrogenation zone wherein the dispersion is subjected to dehydrogenation for about 0.1 to 20.0 seconds, eccting formation of hydrogen and delivering eiuent from the dehydrogenation zone comprising coke and hydrogen to the aforesaid reaction zone to supply heat thereto and maintain uidization therein.

References Cited in the tile of this patent UNITED STATES PATENTS 1,875,923 Harrison Sept. 6, 1932 2,471,104 Gohr May 24, 1949 2,600,430 Riblett June 17, 1952 2,738,307 Beckberger Mar. 13, 1956 FOREIGN PATENTS 709,583 Great Britain May 26, 1954

Claims

1. THE PROCESS OF PRODUCING A SUPERIOR GAS OIL ADAPTED FOR CATALYTIC CRACKING THAT COMPRISES CONTACTING A RESIDUAL PETROLEUM STOCK WITH COKE UNDER FLUIDIZED CONDITIONS AT CRACKING AND COKING TEMPERATURE IN A REACTION ZONE, PASSING COKE FROM THE REACTION ZONE TO A BURNING ZONE IN WHICH THE COKE IS SUBJECTED TO COMBUSTION AT A TEMPERATURE OF AT LEAST 1500* F., WITHDRAWING COKE AT A TEMPERATURE OF AT LEAST 1500* F. FROM THE BURNING ZONE, WITHDRAWING VAPORS COMPRISING HYDROCARBON GAS FROM SAID REACTION ZONE, DISPERSING SAID COKE WITHDRAWN FROM SAID BURNING ZONE IN SAID HYDROCARBON GAS AND PASSING THE DISPERSION THROUGH A DEHYDROGENATION ZONE AT A TEMPERATURE OF ABOUT 1200 TO 2000* F. FOR A TIME OF ABOUT 0.1 TO 20.0 SECONDS EFFECTING DEHYDROGENATION AND FORMATION OF HYDROGEN DELIVERING EFFLUENT FROM THE DEHYDROGENATION ZONE COMPRISING COKE AND HYDROGEN TO THE AFORESAID REACTION ZONE TO SUPPLY HEAT THERETO AND MAINTAIN FLUIDIZATION THEREIN IN AN ATMOSPHERE OF HYDROGEN AND FRACTIONATING EVOLVED VAPORS FROM SAID REACTION ZONE TO SEPARATE SAID GAS OIL.