US2733194A - Method of adding liquid feed to a - Google Patents

Description

Jan. 31. 1956 R. c. WOERNER 2,733,194

METHOD OF ADDING LIQUID FEED TO A FLUIDIZED COKER Filed April 25, 1950 ELUTRIATOR- SUPERHEATER PREHEATER L Rudolph C.Woerner INVENTOR.

ATTORNEYS Unied m. Farm) Refining Company, New York, N Y.", a corporation of Maine ApplicationApril; 25,- 1950, Serial No. 157,871 3 c ims.- or. 202

invention relates to improvements in the coking of hydrocarbon oils by. contacting the coking stock at a coking temperarure with a body of adsorbentcoke particles nia'intained in a fluidized state in a coking reactor from which large coke particles, are selectively withdrawn as formed" by elutriation and from which vapors are recovered overhead. The process is described and claimed in application Serial No. 121,575 of Kenneth M. Watson filed October 15; 1949, now' Patent 2,707,702. The process-has important, advantages in providing continuous cokingwhile. eliminating the difiiculties and cost of solid coke. relmovaliand handling associated with conventional coking operations. My invention concerns a particular system-for. obtainingimproved initial contact and mixing at the cokingstock with the absorbent coke particles. In a particular aspect, it concerns an improvedsystem in which, thecokingstockis. first segregated" into vapor and residualicomponents, the vapor components are directly introduced into the body of coke particles in the reactor so. as to assist fluidization and, the residual components are separately contactedwiththe. coke particles according toith'e improvedmixing. method of my invention.

Successful operation og the Watson. process requires maintenance of good fluidiz'ation of the body of coke particles in the r eactor--so that coke formed from the heavy constituents of the coking stock can be selectively and etliciently absorbed on the coke particles, thus avoiding coking of the walls and plugging of the reactor and so that large coke particles can be selectively withdrawn as coke is formed in the process to maintain the system in equilibrium. The body of coke particles is supported as a dense phase fluidized bed approximating 35 to 45 pounds per cubic foot in density, over a perforated conical grid. Fluidizing medium, usually steam, is introduced below the grid. An elutriator opens into the bottom of the grid and an elutriation medium, usually steam, is supplied at a velocity permitting large particles to settle from the reactor while retaining finer particles within the fluidized body. The preheated stock is sprayed directly into the fluidized body of the coke particles. I have found that spraying the usual coking stock, e.g. a reduced crude oil or heavy residuum, into the large body of coke particles maintained in the reactor often results in localized effects such as insufficient vaporization and agglomeration which interfere with satisfactory fluidization and which can result in losing the bed.

According to my invention, the coking stock is injected into a stream of coke particles which is rapidly circulated from the main body of coke particles in the reactor through a confined conduit. Thus a stream of coke particles may be withdrawn from the bottom of the reactor bed by means of a standpipe and may be returned to the reactor by means of a riser discharging at a point near the top of the bed or into the upper portion of the bed. The coking stock is injected into the bottom of the riser so as to provide additional time factor for completion of the coking reaction. The rapid circulation of the coke particles past the point of feed entry pro- 2 motes rapid and uniform dispersion and distribution of the stock over the coke particles. The ratio of coke to oil obviously may vary considerably but with particular advantageis of the order of about 10:1 to 30:1 by weight.

An additional problem in economically operating a fluidized coking process is the manner of supplyingsuflicient heat to the materials in the reactorto attain optimum reduction of; thec oking stock to cokeboth in terms of rate of reduction and maximum production of distillate oil useful as. a makin charge stock. Thus rateof; coke make and overhead yield depend to a large extent upon high temperature. The coking temperature varies over the approximate range of 800 to 1290 F. but commercial operation is conducted with advantage in the approximate range of.875 to 1050 F; The most con: venient and least costly method of putting the heat into the reactor is by preheating the coking feed stock, after the usual heat exchange, in a conventional fired heater to the desired temperature or slightly above. At the higher temperaturesof, the coking reaction, say 950 to ZGSO R, coking difficulties are encountered inthe heater. in a particularly advantageous operation according to my invention, the coking stock is preheated-to, as high a temperature as possible withoutcoking the heater tubes, e.g. about 950 r i l V a flash chamber. Thehydrocarbonpartial pressure may be lowered by steam introduction to prompteqseparation; The overhead vaporsare superheated to the de gs ired ing temperaturegwi-th minimumflme factonin a second fired heater. The superheated are introduced. to the coking reactor so as to assist in fluidizing the'body of coke particles maintained therein. Thus the vapors are introduced below the grid or into a lower portion or the reactor bed. The heavy residuum is injected into the stream of coke particles rapidly circulated through the confined conduit from the bottom of the reactorbed to the top of the bed. r I

In this manner, i obtain segregation of the coking feed'stcck so as to permit superheating the light oil com:- ponents at alow residence time minimizing heater g in rd ro pp d ional: a wvthe ma eri s a. coking reactor. The superheated vapors assist in fluidization and thus afford a substantial reduction in the requirements for fluidizing steam. Advantageous vapor phase coking of the light oil components also is accomplished. Improved mixing in terms of faster and more uniform contacting between the heavy oil components and the absorbent coke particles is obtained.

My invention will be further described with reference to the accompanying drawing which represents conventionally and somewhat diagrammatically a flow plan embodying my invention. The coking stock is introduced to preheater 10 and through line 11. Preheater 10 represents a conventional fired heater of the horizontal or vertical tube or coil types. The preheated coking stock is flashed from line 12 into flash chamber 13. Steam is introduced to the flash chamber through line 14 and the overhead vapors are removed through line 15. The light oil components of the coking stock comprising the overhead stream are superheated to the desired coking temperature, e. g. about l,000 to 1100 F. in superheater 16 and from line 17 are passed into coking reactor 18. The superheated vapors are introduced below grid 19 above which a large body of coke particles is maintained in a fluidized state. Reaction vapors are removed overhead from coking reactor 18 through line 19a and large coke particles are selectively removed from.- the bottom of the bed by means of elutriator 20 into which steam is introduced by connection 21 for elutriation. A stream of coke particles is circulated from the bottom of the body of coke particles in the reactor through a confined conduit system comprising standpipe 22 and riser 23 back to a point F., and the preheated stockis flashed innear the top of the main body of coke particles. The heavy residuum separated in flash chamber 13 is conducted by line 24 under control of flow rate and level controller 25 to the bottom of riser 23 where it,is injected into the stream of circulating coke particles through connection 25a. Dispersion steam may be injected with the oil by means of connection 26 in order to promote dispersion of the heavy residuum. Where preliminary segregation of the coking stock to light and heavy oil components is not desired, the preheated coking stock may be directly charged to riser 23 through connections 27 and 25a. Fluidizing steam is introduced below grid 19 of the reactor 18 through connection 28. The reaction vapors removed through line 19a are conducted to a fractionating system (not shown) and may be passed through an internal or external cyclone system to remove entrained coke fines.

In a typical operation, the reactor may be charged with to 30 mesh coke particles to form a bed of about feet by 50 feet, and the reaction is conducted at about 1000 F. Fluidizing medium is supplied to obtain a velocity of 2 to 3 feet per second through the bed and elutriating steam is supplied at about a linear velocity of 35 feet per second. A reduced crude is charged to the system at the rate of about 100,000 pounds per hour and is preheated to about 950 F. before flashing into the flash chamber in the presence of steam charged at the rate of about 10,000 pounds per hour. Overhead at the rate of about 80,000 pounds per hour is superheated to upwards of 1000" F. before charging to the reactor. Heavy residuum at the rate of 20,000 pounds per hour is charged with dispersion steam into the conduit through which coke is circulated at a rate producing a coke to oil ratio of between about 10:1 and 30:1.

I claim:

1. In the coking of hydrocarbon oils by contacting the coking stock at a coking temperature with a body of 4 the circulating stream and charging the admixed stream to the upper portion of the reactor.

2. The improvement of claim 1 in which the ratio of coke to coking stock in the circulating stream is about 10:1 to 30:1 by weight.

3. In the coking of hydrocarbon oils by contacting the coking stock at a coking temperature with a body of coke particles maintained in a dense fluidized bed in a coking reactor from which net coke make is continuously withdrawn selectively as large particles by elutriation and vapors are recovered overhead, the improvement which comprises preheating the coking stock to about 950 F.,

, flashing the stock in a flash chamber, superheating the coke particles maintained in a dense fluidized bed in a coking reactor from which net coke make is continuously withdrawn selectively as large particles by elutriation and vapors are recovered overhead, the improvement which comprises separately withdrawing a stream of coke par ticles from the lower portion of the reactor, rapidly circulatingsaid withdrawn stream of coke particles through a confined conduit, injecting heavy oil coking stock into overhead vapors to a high coking temperature at low residence time to minimize heater coking, introducing the superheated vapors to the coking reactor so as to assist in fluidizing the body of coke particles maintained therein, separately withdrawing a stream of coke particles from the lower portion of the reactor, rapidly circulating said withdrawn stream of coke particles through a confined conduit, injecting the residuum from the flash chamber into the circulating stream and charging the admixed stream to the upper portion of the reactor.

References Cited in the file of this patent UNITED STATES PATENTS 2,340,974 Myers Feb. 8, 1944 2,356,717 Williams Aug. 22, 1944 2,378,531 Becker June 19, 1945 2,379,711 Hemminger July 3, 1945 2,394,651 Alther Feb. 12, 1946 2,426,848 Tuttle Sept. 2, 1947 2,427,112 Tyson Sept. 9, 1947 2,445,328 Keith July 20, 1948 2,456,796 Schutte Dec. 21, 1948 2,511,088 Whaley, Jr. June 13, 1950 2,534,051 Nelson Dec. 12, 1950 2,543,884 Weikart Mar. 6, 1951 2,606,144 Leffer Aug. 5, 1952 OTHER REFERENCES Murphee et al.: Journal of the Institute of Petroleum,

vol. 33, N0. 286, pp. 608620.

Coke and Gas, September 1947, pp. 261-266.

Claims (1)

1. 3. IN THE COKING OF HYDROCARBON OILS BY CONTACTING THE COKING STOCK AT A COKING TEMPERATURE WITH A BODY OF COKE PARTICLES MAINTAINED IN A DENSE FLUIDIZED BED IN A COKING REACTOR FROM WHICH NET COKE MAKE IS CONTINUOUSLY WITHDRAWN SELECTIVELY AS LARGE PARTICLES BY ELURIATION AND VAPORS ARE RECOVERED OVERHEAD, THE IMPROVEMENT WHICH COMPRISES PREHEATING THE COKING STOCK TO ABOUT 950* F., FLASHING THE STOCK IN A FLASH CHAMBER, SUPERHEATING THE OVERHEAD VAPORS TO A HIGH COKING TEMPERATURE AT LOW RESIDENCE TIME TO MINIMIZE HEATER COKING, INTRODUCING THE SUPERHEATED VAPORS TO THE COKING REACTOR SO AS TO ASSIST IN FLUIDIZING THE BODY OF COKE PARTICLES MAINTAINED THEREIN, SEPARATELY WITHDRAWING A STREAM OF COKE PARTICLES FROM THE LOWER PORTION OF THE REACTOR, RAPIDLY CIRCULATING SAID WITHDRAWN STREAM OF COKE PARTICLES THROUGH A CONFINED CONDUIT, INJECTING THE RESIDUUM FROM THE FLASH CHAMBER INTO THE CIRCULATING STREAM AND CHARGING THE ADMIXTURES STREAM TO THE UPPER PORTION OF THE REACTOR.

Images