US2755232A - Heat exchange between parallel reaction systems - Google Patents

Description

July 17, 1956 W. J. DOUGHERTY Filed April 26, 1951 HOT CRACKED GAS STREAM PREHEATER RETORT BURNER mucucnso CRACKED GAS s-rncm wzucncn [8 PR EHEATED HYDROGARBON REACTOR LIQUID HYDROCARBON INVENTOR WALTER J. DOUGHERTY ATTORNEY HEAT EXCHANGE BETWEEN PARALLEL REACTION SYSTEMS Walter E. Daugherty, Wilmington, DeL, assignor to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Application April 26, 1951, Serial No. 223,045

9 Claims. (Cl. 196-52) This invention relates to multiple process systems for cracking hydrocarbons wherein continuously circulating contact solids are employed, and more particularly to the conservation of heat during the simultaneous operation of two or more cracking systems, wherein one system is operated at a higher temperature than an associated system.

A typical application of the present invention is its employment with a process for pyrolytic cracking of a gaseous hydrocarbon which is operated simultaneously with a second hydrocarbon cracking process, the latter being conducted at a relatively lower temperature than the former.

One system for pyrolytic cracking of gaseous hydrocarbons comprises subjecting the hydrocarbons to high temperatures for a short time by contact with a hot States Patent invention to provide a process of heat interchange between two or more simultaneously operating cracking systems.

Another object is the economical utilization of the surplus heat available from a relatively high temperature cracking process as a source of heat for a lower temperature cracking process.

A further object is to provide a novel and efficient method of accomplishing the foregoing objectives by suitably conveying, in heat-exchange relationship, the hydrocarbons and contact solids of the two or more systems.

With the above and other objects in view, the invention has particular relation to certain novel features of arrangement of apparatus and use, examples of which are given in the following specification and illustrated in the accompanying drawing in which like reference numerals designate like parts.

The single figure of the drawing diagrammatically illustrates two independent cracking processes which are so associated as to supply the surplus heat from the higher temperature system to the lower temperature system.

Referring now more particularly to the drawing, the letter A designates one independent system employing a process for pyrolytically cracking normally gaseous hydrocarbons such as propane, during the gas lift stage by I contact with hot continuously recycled granular solids.

granular solid. The cracking of gasous hydrocarbons, for

medium having a lower temperature, which in the instant invention is a contact mass employed in a second simultaneously operated cracking system. In pyrolytic cracking systems of the above type the hot contact solids may be continuously recycled, first through a reaction zone and then through a reheating zone. In order to recycle the solids, one successful method employed is that of elevating the solids in the reaction or cracking zone by means of the gaseous hydrocarbons undergoing cracking followed by disengaging the solids and cracked hydrocarbons. The disengaged solids are then allowed to gravitate through a reheating zone with subsequent reelevation in the cracking zone.

In addition to cracking normally gaseous hydrocarbons by appropriate heat treatment, it is also possible to thermally crack normally liquid hydrocarbons. One method for so cracking liquid hydrocarbons comprises initially vaporizing the hydrocarbons followed by passing the vapors in heat-exchange relationship also with hot continuously recycled granular contact solids.

Due to the difference in components between the gaseous hydrocarbons and those hydrocarbons normally liquid, it is possible to thermally crack the latter at a lower temperature than the former. Thus, it will be seen that if the above two systems are operated simultaneously, one being conducted at a higher temperature than the other, a worth-while saving (from a commercial standpoint) may be effected if an eflicient process for conservation of heat between the two systems could be developed.

Accordingly, it is a primary object of the present The letter B designates a system for cracking vaporous hydrocarbons by contact with continuously recycled hot granular solids. As will be developed more fully hereinafter, appropriate means are provided for passing normally liquid hydrocarbons into heat-exchange relationship with the hot used granular contact solids of system A to thereby heat and/ or vaporize them prior to cracking in system B. Further, provision is also made for reducing the temperature of the cracked eflluent of system A by passing the efiluent in heat-exchange relationship with the granular contact solids employed in cracking the vaporized hydrocarbons in system B.

The numeral 1 designates a transfer hopper for collecting particles of hot contact solids flowing by gravity after reheating. A gas feed inlet 2 supplies hydrocarbons in the gaseous state, while a second gas inlet 3 may be used to provide an auxiliary diffuser gas such as steam or an inert gas which will assist the gaseous hydrocarbon in the impelling and elevating of the contact solids.

The gas elevator is designated at 4 and generally comprises a pipe or other hollow member, hereinafter referred to as the lift pipe, and is used to confine the gaseous mixture containing the contact solids during elevation. The elevator 4 discharges into a disengaging chamber 5 wherein the gaseous medium and the contact solids are separated. The contact solids so separated in the disengaging chamber 5 are permitted to flow by. gravity through a line 6 and into a preheater 7. This preheater 7 comprises suitable means for passing, in heat-exchange relationship, the hot contact solids of system A and the incoming uncracked hydrocarbons which supply the second cracking system B.

The numeral 8 designates a retort wherein the contact solids flowing from the preheater 7 are reheated by direct heat-exchange with a heated gas such as that from an airline burner. The heating gas is supplied to the reheating zone through line 9. The contact solids, after reheating, then return to the hopper 1 by means of a discharge line 10. A line 11 conveys the efiiuent cracked gaseous hydrocarbons from the disengaging chamber 5 to a quenching apparatus in system B. From retort 8 an exit line 12 conveys the flue gases from the reheating of the contact solids in system A to gas lift hopper 13 in system B.

System B operates in a manner which is somewhat similar to system A in that the contact solids are continuously recycled with the aid of a gas lift. However, actual cracking is not accomplished in the gas lift stage in system 13.

Designated by the numeral 14 is a lift pipe for confining the mixture of gas and contact solids which, like in system A, discharges into a disengaging chamber 15 wherein the contact solids and gas are separated, the gas being drawn oil by means of line 16 while the contact solids are allowed to flow by gravity through line 17 into the subsequent stages of the system. At the dis charge end of line 17 is a quencher 18 which has provision for passing in heat-exchange relationship the downward flowing contact solids of system B and the effluent cracked gas from system A, the cracked gas being discharged after quenching through line 19. From quencher 18 the contact solids continue downwardly by gravity and pass into reactor 20 where they are contacted with the preheated hydrocarbons to be cracked in system B. From the reactor 29 the contact solids are conveyed to lift hopper 13 through line 21.

As a result of the contact between the hydrocarbons of each system and the hot granular solids during the cracking, and also due to contact between incoming feed for system B and the hot contact solids of system A to be more fully developed hereinafter, formation of coke will develop on the granular solids leading to disruption of the solids flow pattern and decrease in etliciency of heat transfer. Hence, although not specifically shown, it is within the scope of this invention to provide for removal of the coke thus formed. One suitable method may comprise withdrawing a portion of the gravitating granular solids, removing the coke therein by treatment with an oxidizing gas, and returning the regenerated solids to the system.

In operation: a hot gaseous hydrocarbon stream enters hopper 1 where it passes upwardly through lift pipe 4 carrying with it, in intimately dispersed relationship, hot contact solids, such as fuzed alumina particles, whereby, as a result of the intimacy of contact and temperature, cracking of the gaseous hydrocarbon will take place. Upon entering the disengaging chamber 5, the cracked gaseous hydrocarbon will be separated from the hot contact solids, and, while at elevated temperature, will be conveyed to quenching unit 18 where they are passed in heat-exchange relationship with the downwardly flowing contact solids of system B. The contact solids, as a result of the heat-exchange, will take on an increased heat content, the etlluent cracked gaseous hydrocarbons from system A being correspondingly cooled. The cooled gas stream is then discharged and conveyed to subsequent operations. Thus, it will be seen that a large portion of the heat necessary for cracking the hydrocarbons in systcm B will be supplied from the heat content of the cracked hydrocarbon stream from system A.

in addition to the above source of heat, a second source of heat is obtained by passing the hydrocarbon feed for system B in heat-exchange relationship with the hot contact solids of system A in preheater 7. Hydrocarbon feed for system B is initially supplied through line 22 leading to preheater 7, where it absorbs heat from the hot contact solids of system A. Preferably the feed for System B comprises liquid hydrocarbons which are introduced into preheater 7 concurrently with a downwardly moving bed of hot granular contact solids of system .A, resulting in the vaporization of the hydrocarbons and a corresponding increase in heat content. Following this heat interchange, the hot vaporized hydrocarbons are conveyed by line 23 to reactor 20 of system B wherein they may be passed in concurrent flow with the hot descending contact solids therein. As previously indicated, the specific provision for contacting the contact solids and hydrocarbon in system B is not critical to the present invention and may comprise any one of several concurrent or countercurrcnt means.

In order to reheat the contact solids of system A, provision is made for passing the contact solids from preheater 7 through vessel 8, wherein the solids are contacted with hot gas in such a manner that the heat lost to the hydrocarbons in the cracking operation and the subsequent preheating stages is replaced to a substantial extent. The reheated contact solids then pass to hopper 1 for recycling, while the flue gases from the reheating process, rather than being discharged from the system, are conveyed by means of line 12 to hopper 13 of system B, wherein they form the elevating medium for the recycling contact solids and by suitable heat transfer therein supply a portion of the heat to the solids being elevated. The contact solids returned to hopper 1 are thus restored to the desired temperature necessary for cracking and excess sensible heat in the reheating gas is favorably utilized.

According to the foregoing construction and arrangement a cracking system, as represented by A and which is operated at a relatively high temperature, may be used to supply an appreciable portion of the heat necessary for cracking in a lower temperature process as represented by system B.

As an operating embodiment in accordance with the above description, a normally gaseous hydrocarbon feed such as one predominating in propane is introduced at about F. through line 2 into hopper 1. Heated solids from retort 8 are introduced through line 10 at a temperature of about 1800 F. The gaseous hydrocarbon contacts the hot solids in heat exchange relation and simultaneously elevates the solids through conduit 4 while being converted therein to desired products. As a result of heat exchange and conversion conditions the gases and solids emerge from conduit 4 into disengaging zone 5 at a temperature of about 1500 F. The hot gases removed from disengager 5 are transferred through line 11 to quencher 18 of system B wherein the temperature of the gas is lowered to approximately 800 F. by countercurrent contact with the gravitating solids passing therethrough. Solids disengaged in vessel 5 of system A are transferred through line 6 to preheater 7 and therein pass in heat exchange relation with liquid hydrocarbon feed introduced at a temperature of about 100 F. As a result of this heat exchange the solids and hydrocarbons both leave preheater 7 at temperature of about 600 F. The solids having temperature of about 600 F. are reheated by suitable means in retort 8 to approximately 1800 F. for reintroduction through line 10 to hopper 1. The preheated feed from preheater 7 passes to system B through line 23.

Solids from quencher 18 preheated to approximately ]400 F. by reason of heat exchange contact with the hot cracked gas stream from system A enters reactor 20 in concurrent flow relation with the preheated liquid introduced through line 23. By reason of contact of the hot solids with the hydrocarbon feed in reactor 20 desired conversion of the hydrocarbon is obtained with concomitant temperature reduction of the solids. Thus, solids and recovered gaseous products both leave reactor 20 at approximately 800 F. The cooled solids from reactor 20 are transferred through line 21 to hopper 13 wherein they are contacted with an elevating gas and transferred to vessel 15 for return through line 17 to quencher 18. By judicial use of flue gas as the elevating gas introduced through line 12, temperature losses during this transfer process are negligible and the solids enter quencher 18 at approximately 800 F.

The quenched cracked gas stream and the cracked hydrocarbon stream both having temperature of approximately 800 F. are removed for further processing as may be desirable either as a combined stream or separate streams.

A further modification of the instant invention contemplates simultaneously operating a pyrolytic cracking system at a relatively high temperature and a lower temperature catalytic cracking process with similar heat-exchange. In a system of the latter type, a" continuously recycled granular catalyst would be employed and the liquid hydrocarbon feed would be passed in heat-exchange relationship with the contact solids of the pyrolytic system in a manner as mentioned above, resulting in increasing the heat content of the feed and/or vaporization. Due to the constant accumulation of coke on the granular catalyst particles in a catalytic cracking process, provision would also be made for constantly regenerating the catalyst by treatment with an oxidizing gas as is wellknown to those familiar with the art, Thus, in such a system the reactor 20 of system B may be a combination reactor vessel and a catalyst regenerator, or the reactor vessel and regenerator may comprise two independent vessels. Depending on the heat balance of system B when operating as a catalytic process, the cracked gas stream from system A may, as previously mentioned, be passed in heat-exchange relationship with downwardly moving granular catalyst in quenching chamber 18. However, this step will depend on operating conditions as it will be appreciated that a certain amount of heat will be acquired during the catalyst regeneration step. In this connection it may be desirable to pass only the effluent cracked stream from system A in heat-exchange relationship with the catalyst of system B without preheating the feed by means of the contact solids of system A.

It is understood that the foregoing discussion and the drawing are only representative of the instant inven tion and that various modifications may be made without departing from the scope of the invention, which is intended to be limited only by the following claims.

I claim:

1. A method of simultaneously cracking two independent streams of hydrocarbons which includes reacting the streams in independent systems of hot circulating contact solids wherein the said contact solids are continually recycled from a reaction zone to a reheating zone, passing one stream of hot cracked hydrocarbon vapors in heat-exchange relationship with respect to a moving bed of contact solids employed in cracking the other stream of hydrocarbon to thereby provide heat for crack-.

ing the second stream of hydrocarbon.

2. A method of simultaneously cracking two independent streams of hydrocarbons which includes reacting the streams in independent systems of hot circulating contact solids wherein said contact solids are continually recycled from a reaction zone to a reheating zone, passing one stream of hot cracked hydrocarbon vapors in heatexchange relationship with respect to a moving bed of contact solids employed in cracking the other stream of hydrocarbon to thereby provide heat for cracking the second stream of hydrocarbon, and passing the uncracked hydrocarbon of the second stream in heat-exchange relationship with respect to contact solids leaving the reaction zone of said first stream.

3. A method of simultaneously cracking two independent streams of hydrocarbons which includes reacting the streams in independent systems of hot circulating contact solids wherein the contact solids are continually recycled from a reaction zone to a reheating zone, passing one stream of hot cracked hydrocarbon vapors in heat-exchange relationship with respect to a moving bed of contact solids employed in cracking the other stream of hydrocarbon to thereby provide a portion of the heat for cracking the second stream of hydrocarbon, passing the uncracked hydrocarbon of the second stream in heatexchange relationship with respect to the contact solids leaving the reaction zone of said first stream, and then passing the preheated uncracked hydrocarbons of the second stream into contact with the contact solids which have been preheated by said first stream.

4. A method of simultaneously cracking two independ: ent streams of hydrocarbons which includes reacting the streams in independent systems of hot circulating contact solids wherein the contact solids are continually recycled from a reaction zone to a reheating zone, comprising passing a first stream of hot cracked hydrocarbon vapors in heat-exchange relationship with respect to a moving bed of contact solids employed in cracking a second stream of hydrocarbon, thereby providing heat for cracking said second stream of hydrocarbon, passing the uncracked hydrocarbon of said second stream in heat-exchange relationship with respect to the contact solids leaving the reaction zone of said first stream, passing the preheated uncracked hydrocarbons of said second stream into contact with thecontact solids preheated by said first stream, and subsequently conveying the con- 'tact solids employed in cracking said second stream of hydrocarbons to a higher point for recycling by subsequent gravitational flow by a gas stream comprising the flue gases from the reheating Zone of the contact solids cooled by cracking said first hydrocarbon stream.

5. A process of simultaneously cracking a gaseous hydrocarbon stream and a second hydrocarbon stream at a lower temperature than the first stream using two independent moving bed systems of hot contact solids which includes cracking said first stream in a hydrocarbon vapor lift in the presence of hot contact solids, passing the cracked eflluent of said first stream into a quench chamber containing a moving bed of contact solids employed in the second system, passing the second hydrocarbon stream which has been preheated into a reaction zone containing the contact solids heated by said efiiuent, and returning the used contact solids of said second system to said quench chamber by means of a gas lift,

6. A process of simultaneously cracking a gaseous hydrocarbon stream and a second hydrocarbon stream at a lower temperature than the first stream using two indepedent moving bed systems of hot contact solids which includes cracking said first stream in a hydrocarbon vapor lift in the presence of hot contact solids, subsequently passing said contact solids to a reheating zone wherein reheating is effected by combustion of carbonaceous material with the production of flue gas, passing the cracked effiuent of said first stream into a quench chamber containing a moving bed of contact solids employed in the second system, passing the second hydrocarbon stream in a preheated condition into a reaction Zone containing the contact solids heated by said eflluent, returning the used contact solids of said second system to the quench chamber by means of a gas lift and supplying said gas lift with said flue gas from the contact solids reheating zone of the first cracking system.

7. A method of simultaneously effecting independent reactions in the presence of separate systems of continuously recycled contact materials at different temperature levels with increased etficiency in a co-ordinated system which includes effecting a primary reaction in the presence of a primary moving solids contact mass at elevated temperature, passing the reaction products from the primary reaction in heat-exchange relationship with a secondary moving solids contact mass to elfect temperature elevation thereof, effecting a secondary reaction in the presence of the heated secondary contact mass, preheating the charge to the secondary reaction by heat-exchange with the efiiuent primary contact mass from the primary reaction, and subsequently restoring the temperature of the primary contact mass for reuse in the primary reaction.

8. A process of simultaneously cracking a gaseous hydrocarbon stream pyrolytically in a hot circulating contact solids system and a second hydrocarbon stream catalytically at a lower temperature in a continuously recycled catalyst system which includes cracking said first stream in a hydrocarbon gas lift in the presence of said hot contact solids, passing the cracked efiluent of said first stream into a quench chamber containing a downwardly moving bed of catalytic solids employed in cracking the second hydrocarbon stream, passing the second hydrocarbon stream in a preheated condition into a reaction zone containing the catalytic solids heated by said cracked 7 eflluent, recycling said catalytic solids by a gas lift elevating means supplied by gases issuing from the contact solids reheating zone of the first cracking system.

9. A process of simultaneously cracking a gaseous hydrocarbon stream pyrolytically in a hot circulating contact solids system and a second hydrocarbon stream catalytically at a lower temperature in a continuously recycled catalyst system which includes cracking said first stream in a hydrocarbon gas lift in the presence of said hot contact solids, passing the cracked etfiuent of said first stream into a quench chamber containing a downwardly moving bed of catalyst solids employed in cracking the second hydrocarbon stream, preheating said second hydrocrabon stream prior to cracking by passing said stream in heat exchange relationship with the hot contact solids employed in said first system, reheating said contact solids in a reheating zone by combustion of carbonaceous material with the production of flue gas, returning said reheated contact solids to said hydrocarbon gas lift, passing the second hydrocarbon stream in a preheated condition into a reaction zone containing the catalytic solids heated by said cracked efiluent, recycling said catalytic solids by a gas lift elevating means supplied by gases issuing from the contact solids reheating zone of the first cracking system.

References Cited in the file of this patent UNITED STATES PATENTS 2,436,254 Eastwood et a1. Feb. 7, 1948 2,439,730 Happel Apr. 13, 1948 2,443,210 Upham June 15, 1948 2,444,650 Johnson et a1. July 6, 1948 2,448,922 Simpson et al Sept. 7, 1948 2,459,824 Leffer Jan. 25, 1949 2,462,891 Noll Mar. 1, 1949 2,541,693 Frevel Feb. 13, 1951 2,571,342 Crawley Oct. 16, 1951 2,587,669 Weinrich Mar. 4, 1952 2,597,346 Lefier May 20, 1952 2,626,687 Bearer Jan. 20, 1953 2,642,381 Dickinson June 16, 1953 OTHER REFERENCES Houdrifiow, Oil and Gas Journal, pages 78 and 79. Jan. 13, 1949, vol. 47.

Claims (1)

1. A METHOD OF SIMULTANEOUSLY CRACKING TWO INDEPENDENT STREAMS OF HYDROCARBONS WHICH INCLUDES REACTING THE STREAMS IN INDEPENDENT SYSTEMS OF HOT CIRCULATING CONTACT SOLIDS WHEREIN THE SAID CONTACT SOLIDS ARE CONTINUALLY RECYCLED FROM A REACTION ZONE TO A REHEATING ZONE, PASSING ONE STREAM OF HOT CRACKED HYDROCARBON VAPORS IN HEAT-EXCHANGE RELATIONSHIP WITH RESPECT TO A MOVING BED OF CONTACT SOLIDS EMPLOYED IN CRACKING THE OTHER

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