US 2698830 A
Description (OCR text may contain errors)
Jall- 4, 1955 F. J. JENNY 2,698,830
HYDRocARBoN CONVERSION PROCESS Filed oct. e, 195o United States Patent O HYDROCARBON CONVERSION PROCESS Frank I. `lenny, New York, N. Y., assignor to Texaco Development Corporation, New York, N. Y., a corporation of Delaware Application October 6, 1950, Serial No. 188,693
3 Claims. (Cl. 196-67) The present invention relates to a combined gas generation and cracking process, and more specifically involves the continuous and complete conversion of undesired liquid hydrocarbons into desirable liquid and/or gaseous fractions.
In particular, the invention contemplates the consumption to extinction of undesired liquid hydrocarbons in the formation of high quality motor fuel fractions, together with a gaseous residue suitable as a high heating value fuel gas, or alternatively, as a feed stock for the synthesis of liquid hydrocarbons. In this way, the invention provides a process flexibly adapted to the economical conversion of an undesired fraction into high heating value fuel gas and desirable liquid motor fuel, without formation of undesired hydrocarbon fractions, and in particular, without production of undesired coke or solid carbonaceous residue.
Therefore, the present invention is particularly applicable to the treatment of heavy residual stocks which cannot be economically converted by conventional thermal or catalytic methods, and which, therefore, are usually only suitable for heavy fuels, such, for example, as heavy crude residua and heavy residua of catalytic or pyrolytic cracking.
In accordance with the present invention, the liquid hydrocarbon feed, as for example, a heavy residual fuel oil and preferably the lower carbon residue fractions thereof, is injected directly into a substantial stream of partial combustion products issuing directly from a gas generator at a high rate and substantially at combustion temperatures above 2000 F. and up to 3000 F. and above, to effect cracking. Temperature is regulated by controlling the relative rate of hydrocarbon injection, or by suitable temperature moderants such as steam, to maintain a suitable cracking temperature in the range of about 900-1800 F. Preferably, however, the cracking temperature is in the range of about lll500 F. to yield a highly aromatic cracked gasoline fraction. In such case, contact time is advantageously in the range of 1 to seconds.
Hydrocarbon conversion is effected not only in the presence of the substantial flow of partial combustion products but in a refractory-walled reaction chamber defining a free and unobstructed combustion space. Under these conditions, coke or carbon deposition in the chamber is avoided, coking being limited to the form of minute particles entrained in the resulting gasiform stream and carried out of the reaction zone.
The effluent mixture comprising the products of partial combustion and cracking, together with the entrained fine particle, carbonaceous solid, are continuously treated to effect separation between the desired liquid products in the motor fuel boiling range and the heavy, high carbon residue products containing the solid carbon particles. For example, separation is preferably carried out in a countercurrent gas-liquid fractionator, such as a bubble tower, in which the downow of oil reflux continuously scrubs the upllowing gasiform stream, and thereby delivers the entrained fine particles to the bottom of the tower in the form of a slurry in the heavy hydrocarbon residues. In an intermediate portion of the tower, a relatively low carbon residue fraction may be removed and continuously fed to the cracking zone.
The fractionator overhead is composed essentially of valuable motor gasoline boiling fractions together with a gas consisting of the partial combustion products, hy-
drogen and carbon monoxide, together with the light hyresidual stocks to effect a substantial initial separationresidual materials of relatively low value.
2,698,830 Patented Jan. 4, 1955 ICC drocarbon gases. Separation is effected between the normally gaseous and liquid constituents of this effluent, to yield an improved cracked liquid motor fuel fraction and a residual fuel gas of high heating value.
The bottoms slurry of the fractionator composed of suspended solid carbon in the cracking tars and other heavy fractions unsuitable for conventional cracking, provides the charge for the generation of the partial combustion product gas. Therefore, this bottoms fractions is continuously burned with a stream of pure oxygen and added steam to yield a partial combustion product, that is to say, a product gas composed essentially of hydrogen and carbon monoxide. Advantageously, the partial combustion takes place in a refractory-walled generator which, like the hydrocarbon cracking or conversion zone, provides a free, unoccupied chamber, that is to say, a reaction space completely free of packing, checkerwork or any other solid obstructions.
In the presence of pure oxygen, combustion occurs as above indicated, at temperatures above 2000 F. and up to 3000 F. and higher, if desired. The relative proportions of oxygen and carbonaceous feed are regulated to yield essentially or predominantly a gaseous stream of hydrogen and carbon monoxide. As above indicated, this stream, without cooling, passes directly to the cracking zone where it immediately receives the injected hydrocarbon cracking stock.
As previously noted, by virtue of relatively short time, high temperature cracking of the relatively low carbon residue fractions of the feed and the high linear velocity of flowing partial combustion products, the free carbonaceous and coke-like residue of cracking occurs as light, dry, fluffy, solid particles which flow off in entrainment in the cracking zone effluent. Cracking occurs in the presence of a gas which contains substantial proportions of hydrogen which act to further inhibit the formation of coke-like residues and assure that dry, fluffy, solid particles result. Therefore, objectionable coke deposition on the cracking chamber walls is essentially overcome, permitting continuous operation for indefinite periods of time.
It is particularly advantageous in the case of heavy of the feed into relatively low and high carbon residue fractions for introduction respectively, to the cracking and gas generation zones. In accordance with the present invention, this may be accomplished by supplying all or any portion of the incoming feed stock to the above mentioned product fractionator, preferably at a point in the lower section thereof. In this type of operation, the bubble tower, by virtue of the large volume of gases flowing therethrough, serves, in effect, as a distillation unit, the heaviest fractions of the feed stock flowing downwardly to provide additional oil reflux for carbon cleanup, while the lower carbon residue fractions can be withdrawn as a side stream from an intermediate level and passed directly to the cracking Zone. Actually, with a stock of this type, it is preferred to thus treat all the incoming feed stock and continuously supply the partial combustion gas generator and the cracking zone, respectively, with the high carbon and low carbon residue fractions, while the product fractions of gasoline and fuel gas mixture are withdrawn overhead for recovery.
In summary, therefore, the present invention contemplates the continuous separation of process streams into a relatively low carbon residue fraction, continuously subjected to pyrolytic conversion, and a relatively high carbon residue fraction containing tars and solid carbonaceous materials, which is burned with pure oxygen to form hydrogen and carbon monoxide to supply the thermal energy and the physical medium for cracking.
The present invention is, therefore, of particular advantage in that it permits consumption to complete extinction of the feed stock in the formation of valuable desired products and without the objectionable intermediate or final formation of cokes, tars and similar heavy Accordingly, it overcomes the process deficiencies which have hithertofore prevented economical disposition of undesirable rheavy residual stocks. This follows from the fact, explained above, that the objectionable products are continuously handled in fluid streams and consumed by combustion.
Another particular advantage of this invention is its flexibility, by Virtue of which substantially the entire product may be converted 'into'desired proportions of desired liquid and gaseous'products. For example, the 'fuel gas mixture may be'readily. separated intona synthesis gas mixture of hydrogen and carbon monoxide 'suitable for directxcatalytic conversion tinto 'synthetic hydrocarbons, an olefin fraction suitable 'for conversion intol polymer gasoline and a residual light hydrocarbon `fraction which can be recycled as a feed to the partial combustion zone. Any normally gaseous or relatively heavy -residues of polymerization or hydrocarbon synthesis may also be consumed by partial combustion,'thus forming additional synthesis gas charge for the production of synthetic hydrocarbons.
In order to describe more specifically the invention, reference is had' to the attachedflow sheet, wherein a suitable high carbon residue feed stock enters from any source not shown,` through pipe 10, and. passes `successively through heating exchangers 12V and 13.
In accordance with one embodiment of the present invention, the stock continues through externally tired, indirect heat exchanger 14, where it is raised to a temperature of, for example, about 600 F., and thereafter passes .through pipe 15 into 'the lower portion ofthe cracking zone 17, as indicated.
It is particularly important .tonote that the cracking zone`17 is an open, free, Vunobstructed chamber, lined with suitable refractory material, but significantly free from any internal packing, checkerwork kor obstructions of any kind whatsoever. The lower portionof the cracking chamber continuously receives a substantial stream of freshly generated partial combustion gas comprising essentially hydrogen and carbon monoxide, at an elevated temperature above about'2000 F. and up to 3000 F. and higher, .to be hereinafter described in greater detail.
'The rate of oil injection through line 15 issuch as .to maintain an appropriate cracking temperature of, for example, about l100 F. Therefore, cracking ofthe injected oiltakes place withina substantial carrier stream of partial combustiongases. Contact time is relatively brief, as for example, l to seconds, and accordingly, .solid carbon formation is restricted to particles which remain entrained in the effluent product mixture of cracking product-and carrier gas.
Small amounts of oxygen and/or steam. may advantageously be introduced,. either continuously or periodically, to-.thecrackingzone vthrough pipe 16 to .facilitate the cracking operation as ydescribed above.
The cracking product continuously ows through transfer pipe 18, is reduced-appropriately below the cracking range yin cooling exchanger 19, as for example, to. about 650 F., andthe relatively. cooled stream thereupon passes .into the lower portion of fractionator 20. Asabove indicated,. fractionator .20 is preferablyY ofthe bubble` tower type, operating to deliver overhead .motor gasolineand all lighter fractions,land to discharge a bottoms of tars and other heavy, high carbon residue liquids Aunsuitable for cracking. Reboiler 21 isadvantageously provided in the bottom .of the tower. Downow of oil reflux in the tower scrubs and. entrains the sold .particle carbon out of the gasiform tower feed, delivering it as an loil slurry in the withdrawn bottoms fraction. To improve this'effect, :a side stream .mayV be withdrawn from-.the .tower through line 31, pump 32 .and .indirect heat exchanger 13, and after further coolingin exchanger 33, returned .to a higher point in jthe tower foradditional reuxing.
'The overhead efiiuent from ,the tower 20, at a temperature. forexample, of about 450 F., moves by way of transfer line 341through aforementioned exchanger 12 where Vit .is cooled by indirectly transferring heat to the incoming stock, and .thence passes .through condenser 35, if necessary, into a decanter 36. Condensed moisture, if any, is withdrawn from the bottom of -the decanter through line `7, whereas the liquid .hydrocarbon condensate is withdrawn through intermediate pipe 39.
A portion of the withdrawn hydrocarbon condensate passes through branch pine 4t) into the upper portion of tower 20 as a top reflux. The remainder continues through pipe`39 into stabilizer or other suitable treatment and recovery'facilities 41. The stabilizer discharges a final product gasoline through pipe 42, while residual normally gaseous hydrocarbons pass through line 43 and are admixed with the normally gaseous overhead from the decanter 36 withdrawn through pipe'44. 'The resulting gas mixture is delivered to an appropriate treatment and recovery system 45, delivering through outlet pipe 46 an ideal high heating value fuel gas mixture composed essentially of hydrogen, carbon monoxide and normally gaseous hydrocarbons. Any normally liquid hydrocarbon residue passes via pipe 47 into the gasoline delivery pipe 42.
The oil slurry bottoms from the fractionator tower 20 continuously discharges through pipe 22 and branch pipe into a burner nozzle 24, feedingv the gas generation chamber 23. Burner nozzle 24, which may take any suitable form, is also supplied, from any suitable source not shown, with a stream of substantially pure oxygen through pipe 26.
By substantially pure oxygen is meant a gas stream predominantly oxygen, and preferably oxygen which is substantially free from contaminants, that is, a molecular stream containing at least percent oxygen and preferably above percent oxygen, such as may be readily produced by the liquefaction and rectification of air.
Provision may advantageously be made in the form'of pipe 23 for introduction' of `regulated quantities of steam into gas generation chamberV 25 from any suitable source, not shown, in order'to permit close temperature control in the gas generation zone 25 and also, where desired,to increasethe proportion of hydrogen formed therein. Alternatively, the steam may be introduced into the burner 24 with the oxygen stream er through special steam passages which, per se, form no part of the present invention, and therefore, are not disclosed in detail.
The combining ratio -of oxygen and carbonaceous'maferial is regulated to yield a partial combustion product composed predominantly or essentially ofhydrogen and carbon monoxide. This means that the atomic O/C ratio of the combined feeds is less than about 2:1, and preferably 'in the vicinity of about 1:1 to about 1.511. As previously stated, combustion takes place at high temperature and the resultant product passes'without cooling through the constriction 30 into the cracking chamber 17, contacting the injected cracking stock, thermally converting .it into desired products of reaction and yielding a combined effluent which passes into .the lower `portion of separating tower 20.
In accordance with one .important feature of the present invention, the separating tower 20 is provided with means for withdrawing a side stream of relatively low carbon residue liquid fractions at an intermediate elevation, as additional cracking feed stock. To this end, a suitable side stream passes through drawoff tap 43 into side stripper 49, the light overhead being returned to the tower through transfer line 50. The stripped side stream flows from the bottom of the stripper through line 51 and preheater 52 into pipe 15 for injection into the cracking zone 17. Preheater 52 permits increasing the quantity of cracking stock fed to the cracking zone without reducing the temperature thereof, and accordingly may be employed to preheat the feed to any required temperature up to about. 1000 F.
In accordance with another important feature of the present invention, the incoming, preheated, fresh feed to the system in pipe 10, after passingthrough the exchangers 12 and 13, passes through branch pipe 53 into the lower section of the tower 20, where, as above indicated, a fractionation thereof occurs, in which the relatively high carbon residue fractions thereof, unsuitable for cracking, pass into the tower bottoms affording additional scrubbing of the upflowing gases and thereafter flowing to the gas generator 2S through line 22. The lighter fractions, in the presence of the large volume of uptiowing vapors and gases are effectively fractionated and withdrawn in the gasoil side stream, supplying the cracking zone through line 51.
This operation is particularly applicable to the treatment of heavy hydrocarbon residual stocks, in which case all of the incoming feed advantageously enters the towe through pipe 53 and is treated in this manner. Accordingly, under such conditions, the tower 20 operates continuously to classify or separate both the incoming feed and the cracking products into a fraction which is subiected to cracking and a bottoms slurry of poor cracking characteristics, which is supplied as a feed to the generator. ln order to balance operation of the cracking and gas generation zones, a portion of the feed may be passed from line into line 23 via dotted line 55. In this' mani ner, sufcient partial combustion gas is assured to prevent objectionable carbon deposition in the cracking zone 17.
In accordance with one embodiment of the present invention, a 45 percent Gach Saran residuum in the quantity of about 20,000 bbls. per day with a Conradson carbon residue of 10.7, is preheated to a temperature of about 600 F. and charged to the oil cracking zone of a combination gas generator-oil cracker, as described above.
The partial combustion gas generator section of the combustion gas generator-oil cracker is continuously supplied with about 88,000 pounds per hour of a bottoms tower slurry of residual gas oil, tar, coke, etc., to be hereinafter described in greater detail. This charge is introduced through a mixing burner together with 3,665 mols per hour of rectified oxygenY of about 95 percent purity (about 1400 tons oxygen per day) and about 4000 mols per hour (72,000 pounds per hour) of steam.
As a result, the generator operates at about 2500 F., yielding a gas consisting essentially of hydrogen and carbon monoxide, with minor proportions of carbon dioxide and unreacted steam.
This effluent gas stream at the combustion temperature ows directly into the cracking zone where it meets the injected cracking stock, thereby continuously maintaining in the cracking zone a temperature about l100 F. Pressure in the cracking and gas generation zones is about 450 p. s. i. g.
The gas generation zone, as above indicated, is an open, unobstructed, refractory lined chamber and has a volume of approximately 1000 cu. ft. Reaction time in the cracking Zone is approximately two seconds and the linear velocity of the combined gas stream at the top of the cracking zone is approximately five feet per second.
In the cracking zone, therefore, the residuum is thermally cracked, in the presence of the carrier stream of partial combustion products, to form gas, gasoline, gas oil, tar and tine particles of entrained coke.
The resulting combined stream from the cracking zone passes into a bubble tower fractionator operating to deliver overhead motor gasoline fractions and lighter fractions. This overhead is condensed to yield a high quality gasoline fraction. The residue is composed essentially of a mixture of hydrogen, carbon monoxide and gaseous hydrocarbons.
In accordance with the present embodiment, the C4 and about one-half the C3 olefins are separated and polymerized to form an additional high quality polymer gasoline. This results in a volumetric yield of total high quality gasoline in excess of 50 percent of the feed stock, plus a yield of approximately 5000 cu. ft. of 500 B. t. u. fuel gas per barrel of charge stock.
The bottoms of the bubble tower fractionator comprising the fractions heavier than motor gasoline, namely, gas oil, tars and scrubbed coke particles, provides the aforementioned bottoms tower slurry which is charged to gas generation zone. Approximately 80 per cent of this stream flows to the gas generation Zone burner, the remainder being used for process fuel requirements.
The bottoms slurrv charged to the gas generation zone comprises about 88,000 pounds per hour of scrubbed, solid carbonaceous cracking residue and heavy liquid hydrocarbon resduum.
Over long, indefinite periods of operation, there is no material coke or carbon deposition in the cracking zone or the transfer lines therefrom and essentially all of the solid carbonaceous material formed by cracking is cycled in the fluid slurry feed to the generator.
Elimination of the step of separating and polymerizing the gaseous oleiins described above results in sacrificing approximately 1125 barrels per dav of polymer gasoline with a commensurate increase in yield of fuel gas having a heating value of about 600 B. t. u. per cubic foot.
In either case, however, the hydrogen and carbon monoxide fraction of the residual gas may be separated and converted into additional liquid hydrocarbons.v This may be accomplished by passing the hydrogen and carbon monoxide mixture in contact with the hydrocarbon synthesis catalyst, such as a metal of the iron group, at an elevated temperature, in a known manner which, per se, forms no part of the present invention. The net result of such treatment is to enable the production of yet increased quantities of motor gasoline fractions.
As indicated in the above example, partial combustion and cracking lare both preferably effected 'at pressures within the range of 0-600 p. s. i. g., preferably 20G-500 p. s. 1. g.
As previously mentioned, maintenance of a substantial flow of partial combustion gas through the cracking zone is critical from the standpoint of obviating objectionable coke deposits. To this end, the linear velocity of the partial combustion or carrier gas is continuously held in the range of 1/2 to l0 feet per second, preferably 1 to 6 feet per second.
Another important feature of the present invention hereinbefore referred to involves the production of predominantly aromatic, cracked motor gasoline fractions, by continuously observing cracking temperatures in the range of about 1100-1500" F. and contact times in the range of 1 to 10 seconds.
The term high carbon residue as used herein refers to stocks which are relatively unsuitable for cracking and are therefore more advantageously consumed in the gas generation zone. The low carbon residue stocks referred to are those having a relatively lower carbon residue value which yield substantial proportions of cracked motor gasoline fractions by the pyrolytic steps disclosed herein. In general, streams with a Conradson number below about 5 fall within the latter category, while those with a Conradson number materially above 5 are generally considered to be high carbon residue materials.
While the invention has been described specifically in terms of the consumption of heavy residual stocks not amenable to effective processing by ordinary catalytic or pyrolytic methods, nevertheless,I the invention is broadly applicable to the processing of other hydrocarbon fractions. In general, where, for example, a relatively light gas oil is employed, initial fractionation of the fresh feed stock may be avoided, the stock passing directly to the cracking zone in accordance with the first described embodiment.
Obviously, many modifications and variations of the invention above set forth may be made without departing from the spirit and scope thereof, as will be apparent to those skilled in the art from the foregoing, and therefore, only such limitations should be imposed as are indicated in the appended claims.
l. In a process for the thermal cracking of a heavy hydrocarbon liquid wherein said hydrocarbon is introduced into a iiowing stream of hot gas comprising carbon monoxide and hydrogen to effect cracking, the improvement which comprises introducing said hydrocarbon into a flowing stream of hot gas consisting essentially of carbon monoxide and hydrogen in a cracking zone, maintaining a temperature within the range of 900 to 1800 F. and a residence time within the range of 1 to 10 seconds in said cracking zone so that lighter hydrocarbons and a solid carbonaceous cracking residue are formed, maintaining a velocity within said cracking zone of from 1/2 to 10 feet per second sucient to entrain said solid residue in said gas stream, passing the resulting effluent product from said cracking zone directly toga rectification, zone wherein a high boiling fraction containing said solid cracking residue is separated from gases and lighter hydrocarbon fractions, passing said high boiling fraction containing said solid residue as a slurry to a gas generation zone separate from said cracking zone, effecting substantially complete reaction of said slurry with substantially pure oxygen at a reaction temperature above about 2000 F. in said gas generation zone to produce a hot gas stream consisting essentially of hydrogen and carbon monoxide, and continuously supplying said mixture of carbon monoxide and hydrogen from said gas generation zone at substantially said reaction temperature directly to said cracking zone as said stream of hot gas.
2. A process as defined in claim l wherein the linear velocity of said stream of carbon monoxide and hydrogen through said cracking zone is within the range of from 1 to 6 feet per second, and the temperature within said reaction zone is maintained within the range of from about 1100 to about 1500 F.
3. A process for the thermal cracking of a hydrocarbon liquid which comprises introducing said hydrocarbon into a flowing stream of hot gas comprising carbon monoxide and hydrogen in a cracking zone to effect cracking, maintaining a temperature within the range of 900 to 1800 F. and a residence time within the range of 1 to l0 seconds in said cracking zone so that lighter hydrocarbons and a solid carbonaceous cracking residue are formed, maintaining a velocity Within said cracking zone of from 1/2 to 10 feet per second sufficient to entrain said solid residue in said gas stream, passing the resulting eiuent product of said cracking zone directly to a rectication zone, introducing a heavy hydrocarbon liquid feed into said rectification zone, contacting said euent product of said cracking zone with said hydrocarbon liquid feed in said rectication zone, separating from the resulting mixture in said rectification zone a gaseous fraction comprising normally gaseous components of said mixture,- separating from said mixture a fraction of intermediate boiling range comprising at least a portion of said hydrocarbon fee'd and introducing said fraction of intermediate boiling range into said cracking Zone as said hydrocarbon liquid, separating from said mixture in said rectication zone a high boiling fraction containing said solid carbonaceous cracking residue, subjecting said high boiling fraction to reaction withV substantially pure oxygen at a temperature above about 2000 F. in a separate gas generation zone to produce a hot gas stream consisting essentially of hydrogen and carbon monoxide, and continuously supplying said gas stream from said gas generation zone at substantially the reaction temperature thereof to said cracking zone as the source of carbon monoxide and hydrogen therefor.
References Cited in the fil/e of this patent UNITED STATES PATENTS 1,459,156 Knibbs June 19, 1923 1,942,191 Steere Jan. 2, 1934 21,074,196 Weber et al. Mar. 16, 1937 2,244,636 Atwell June 3, 19,41 2,399,540 Carr Apr. 30, 1946 2,605,215 Coghlan July 29, 1952