US2692225A - Residuum cracking in a pebble heater - Google Patents

Description

1954 R. A. FINDLAY RESIDUUM CRACKING IN A PEBBLE HEATER Filed Sept. 11, 1950 2a 3;; PRODUCT TO RECOVERY STEPS |I| ll 26 1 39 .l 19 27- J; l4 24 4 FLUE cAs x 42 LIFT cAs INVENTOR. R A. FINDLAY BY 7A A TTORNE Y5 Patented Oct. 19, 1954 RESIDUUM CRACKING IN A PEBBLE HEATER Robert A. Findlay, Bartlesville, Okla. assignor to Phillips Petroleum Company, a corporation of Delaware Application September 11, 1950, Serial No. 184,233

6 Claims. 1

This invention relates to cracking of heavy residual hydrocarbons in a pebble heater.

Pebble heater type apparatus is finding increasing favor in effecting the conversion of various types of hydrocarbon streams into more desirable hydrocarbons, particularly hydrocarbon conversions involving cracking and reforming. Typical pebble heater operation entails heating a gravitating mass of refractory pebbles in an upper heating chamber by contact with hot flue gas formed in the bottom of the chamber by combustion of a light hydrocarbon fuel with air, gravitating the resulting hot stream of pebbles through a restricted pebble throat or passageway into a lower chamber wherein the hot column of pebbles is contacted in countercurrent flow with a stream of hydrocarbon vapor under conversion conditions of temperature, time, and pressure. The stream of pebbles emerges from the bottom of the reactor or furnace consider:- ably cooled and flows downwardly to the lower end of a pebble elevator which elevates the pebbles to a chute leading into the upper part of the pebble heating chamber through which they are delivered to be reheated. In this manner heat is imparted to the refractory pebbles which are utilized to carry the heat for the process to the conversion chamber. In this type of operation as contrasted with hydrocarbon conversion in a regenerative furnace, the flue gas for the process is not mixed with the hydrocarbon product and it is also possible to operate continuously onstrean'l in the conversion of the hydrocarbon.

lhe term pebble as referred to throughout the specification includes any particulate refractory contact material of suitable form, size, and densit to be readily flowable through the pebble heater chambers and capable of withstanding temperatures upwards of 250 0 F. The pebbles are preferably spherical and range from r; to 1" in diameter. Uniform shapes and sizes are preferred but pebbles of irregular shapes and sizes are operable with less efficient results. Common materials utilized in forming pebbles include alumina, mullite, zirconia, thoria, periclase, synthetic and natural clays, either alone or in combination with each other.

For some time one of the problems of the petroleum industry has been to utilize the overabundance of heavy residual hydrocarbons resulting from petroleum processing. It is this problem with which the invention is concerned. a The principal object of the invention is to provide a process for converting heavy residual hydrocarbons to lighter, more valuable hydrocar icons in which all of the heat requirements of the process are obtained from the residual hydrocarbon. It is also an object of the invention to provide a method for removing entrained undesirable tars and carbonaceous constituents from a hot hydrocarbon eilluent so as to reduce and minimize formation of emulsions and coking troubles in later separation and recovery steps. Another object is to provide a process which utilizes the least valuable fraction of a heavy residuum. A further object is to improve the efficiency of a process for the conversion of heavy hydrocarbons in a pebble heater. Other objects of the invention will become apparent from a consideration of the accompanying disclosure.

In accordance with the invention, a heavy hydrocarbon residuum boiling at a temperature upwards of 500 F. is cracked by introducing the feed in liquid form into the upper section of a pebble heater reactor where it is contacted with a gravitating contiguous stream of hot pebbles at a temperature in the range of 1006 to 1700 F. The pebbles are heated in a chamber, directly above the reactor. by burning oil the tar and coke deposited on the pebbles with a stream of air introduced to the bottom of the chamber. The coke and tar referred to are deposited on the pebbles at least in part in the reactor, the balance being deposited on the pebbles in a quench chamber positioned directly above the pebble heating chamber just referred to. In this uppermost quench chamber the pebbles are contacted with the hydrocarbon effluent from the reactor under conditions such that an amount of heavy tar and other heavy hydrocarbon material in the effluent hydrocarbon stream is deposited on the pebbles which, taken with the coke deposited on the pebbles in the reactor, supplies the required heat for the pebble heating step when burned off with air in the middle chamber of the system. In this manner the uppermost chamber acts as a quenching chamber for the hydrocarbon product stream, thereby recovering from this stream a substantial portion of thefuel requirements of the process as well as a considerable portion of the sensible heat of the product stream. The removal of entrained heavy hydrocarbon from the product stream passing through the quench chamber is a distinct aid in the succeeding product separation steps since it practically eliminates the formation of emulsions and coking dimcultie's in the product separation equipment.

7 Temperature conditions in the quench chamher are controlled indirectly by spraying water or passing steam into the bottom of the reactor so as to decrease the temperature of the outgoing pebbles to the range of 500 to 800 F., this temperature being controlled by the amount of water or steam introduced at this point. The pebbles enter the quench chamber at a temperature in this range or slightly below, due to unavoidable heat losses in the elevator equipment, and by diverting a portion of the pebble stream directly into the pebble heating chamber it is relatively easy to control the quench zone temperature so as to deposit the required amount of carbonaceous material on the pebbles which, taken with the coke thereon, supplies the entire heat requirements of the process.

It has been found desirable to introduce steam 7 either with the hydrocarbon feed or separately into the top of the reactor so as to assist in vaporizing the feed and simultaneously reduce the coke formation in the top of the reactor. The steam admitted to the bottom of the reactor not only functions to control outgoing pebble temperature, but also assists in flushing the pebble stream, thereby removing at least a portion of the hydrocarbon therefrom.

' It has been found feasible to utilize inert gases and normally gaseous hydrocarbons as the coolant and flushing gas in the lower section of the reactor. Gases such as nitrogen, C0, C02, methane, ethane, and propane are suitable for this purpose. When operating in the higher temperatures of the cracking range utilized, the use of propane as a flushing gas results in some conversion and reforming involving propane.

The heat required for the steam fed into the reactor both at the top and bottom is preferably obtained by means of a waste heat boiler through which the flue gas from the pebble heating chamber is passed so as to recover available It has been found necessary to utilize a feed to the process which boils at a temperature of at least 5il0 F. in order to make it possible to deposit sufiicient heavy carbonaceous materials on the pebbles in the reactor and in the quenching chamber to furnish the fuel requirements of the process. With thistype of feed it is practical to maintain combustion temperatures in the pebble heating chamber up to at least 2000 F. Since the temperature of the pebbles entering the reactor must be in the range of 1000 to 1700 F., this combustion temperature is ample. The pebble circulation rate required for the process utilizing alumina or mullite pebbles ranges from 40 to 75 pounds per pound of oil fed to the process, depending upon the type of feed and other operating conditions.

' For a more complete comprehension of the invention, reference may be had to the drawing whichis a diagrammatic elevational view of one arrangement of apparatus for performing the invention. The apparatus comprises a series of 3 vertically aligned interconnecting pebble chambers arranged for gravitational flow therethrough. Lowermost chamber II is a reaction chamber having a feed inlet line l2 terminating 4 in a spraying means for dispersing a liquid feed to the reactor. An inwardly and downwardly sloping circumferential baflie I3 is positioned intermediate the ends of the reactor to provide a vapor space between the baffle and the wall of the reactor with which efiluent line [4 communicates for withdrawing reaction products. Lines l6 and I1 communicate with the upper and lower ends of the reactor, repectively, for feeding steam to the upper end and a coolant and flushing gas to the lower end. A steam line I8 from waste heat boiler I9 connects with lines l6 and I1 for delivery of steam to the reactor. Line 2| connects with line H for delivery of water or other coolant and fluid flushing material to the r reactor when it is desired to use such in preference to steam.

Intermediate chamber 22 functions as a pebble heating chamber to which air is supplied through line 23 leading into the lower end of the chamber. Under high temperature conditions the air burns oh the coke and carbonaceous material on the pebbles passing through the chamber forming hot combustion gas which passes upwardly through the chamber and is taken off through line 2-4.' Line 2 1 passes through waste heat boiler It to supply the heat for the steam for the process.

Pebble chamber 26 functions as a product quenching chamber and collects tarry and other carbonaceous materials contained in the efiluent product gas. the cooler pebbles which carry this combustible material into the pebble heating chamber below. Effluent line Hi from reactor ll enters the lower portion of the quenching chambercon- .necting with a distributing conduit 21 therein.

The quench product gas egresses from the quenching chamber through line 28 passing to suitable product recovery apparatus. a Interconnecting throats 3i and 32 serve pass pebbles in a compact stream from one pebble chamber to another. Pebble circulation through the system is controlled by pebble feeder 33 positioned in pebble efiiuent conduit 34 leading from the bottom of reactor ll. Pebble feeder 33 may be any type of conventional feeder which may be controlled to feed pebbles at any desirable rate into gas lift 36 through which a suitable lifting gas such as steam is constantly passed so as to elevate the pebbles fed into the lift to a surge chamber 31 positioned at an elevation above chamber 26 so that pebbles can be gravitated thereto through chute 38 and to pebble heating chamber 22 through chute 39. A pebble feeder M in line 39 functions under the controlof temperature controller 42 which is re bles from line 34 to surge chamber 31 is Within the scope of the invention.

Specific example A heavy fuel oil having an A. P. I. gravity of 15 is processed by the method of this invention in the apparatus shown in the drawing. The

Thesematerials are deposited on' feed, at temperature of 100 F., is introduced into the upper portion of the cracking zone concurrent with pebbles entering from the pebble heating zone at a temperature of 1150 F. Re action products leave the reaction zone at a temperature of 1050 F., and are passed to the quench zone where they contact a portion of the recirculated pebbles, which are at a temperature of 800 F. Vaporous products leaving the quench zone, at a temperature of 850 to 950 F., comprise gaseous to high boiling liquid hydrocarbons in approximately the following proportions:

Product: Wt. percent Gas (C4 and lighter) 30.4 Gasoline (C5-400 F.) 21.0 Gas oil MOO-900 F.) M. 22.5 Heavy oil (900-1150 F.) 26.1

Total 100.0

Higher boiling reaction products not carried out of the quench zone in the vapor stream are condensed on the pebbles and carried into the combustion, or pebble heating, zone. There these materials, together with carbon deposited on the pebbles in the reaction zone, are burned with air to supply all of the heat required in the process. The carbon deposition amounts to from 16-1'7% of the feed.

The pebbles leaving the cracking zone are quenched by a Water spray to a temperature of 800 F., the resulting steam passing out of the chamber with the hydrocarbon products. The pebbles are elevated to a surge zone where they are divided into two streams, about passing to the quench zone, as described above, and the remainder directly to the pebble heating zone.

In another arrangement of apparatus for effecting the process of the invention, quench chamber 20 is positioned opposite heating chamber 22 and reactor H so that a short product effluent line (line H) connects reactor l I with quench chamber 26. This arrangement requires an elevator such as that shown in the drawing and an additional elevator disposed so as to receive pebbles from the lower section of the quench chamber and to deliver them to a chute leading into heating chamber 22 or to a surge chamber similar to chamber 31 disposed at a level above the pebble inlet to chamber 22. This modification of the apparatus is advantageous in that it shortens eflluent line H! but it entails more complicated and expensive pebble transfer.

The illustrative details set forth herein are not to be construed as imposing unnecessary limitations upon the invention, the scope of which is set forth in the claims.

I claim:

1. A process for cracking a heavy residual hydrocarbon which comprises gravitating a stream of hot refractory pebbles through a series of separate connecting zones comprising a pebble heating zone, a cracking zone, and a product quenching zone; introducing a stream of liquid heavy residual hydrocarbon boiling at a temperature of at least 500 F. to the upper end of said cracking zone and contacting the hot pebbles in said cracking zone in concurrent flow so as to raise same to a cracking temperature in the range of 1000 to 1700 F. under conditions which effect cracking of said hydrocarbon and deposition of coke on said pebbles; withdrawing an efiluent hydrocarbon stream of cracked product from an intermediate section of the pebble bed in said reaction zone below the level of feed introduction; contacting the pebble stream in the lower section of said recation zone with a relatively cool gas so as to reduce the temperature of the outgoing pebbles to the range of 500 to 850 F.; transferring a first portion of the pebbles from the bottom of the reaction zone to the top of said quenching zone; contacting the pebbles in said quenching zone in countercurrent flow with said effluent hydrocarbon stream from said reaction zone so as to quench said product stream and deposit heavy tarry constituents of said stream on said pebbles in an amount which when burned in said pebble heating zone with said coke furnishes the entire heat for heating said pebbles; transferring pebbles from the bottom of said quenching zone to the top of said pebble heating zone; transferring a second portion of said pebbles from the bottom of the reaction zone directly to said pebble heating zone; burning off the tarry deposit and coke on the pebbles in said pebble heating zone with a stream of air so as to heat said pebbles to said cracking temperature solely by the heat of combustion of said tarry deposit and coke; and recovering the quenched product.

2. The process of claim 1 in which the proportion of pebbles passing to said quenching zone is regulated in response to variations in temperature from a predetermined temperature in said pebble heating zone.

3. The process of claim 2 in which the propor-- tion of pebbles passing to the quenching zone is maintained in the range of 5 to 50 per cent of the amount circulated.

4. The process of claim 1 in which said relatively cool gas is steam.

5. The process of claim 1 in which said relatively cool gas is a normally gaseous hydrocarbon.

6. The process of claim 1 in which a fixed proportion of the pebbles circulated is passed through said quenching zone and the temperature of the efiiuent pebbles from the pebble heating zone is regulated by controlling the amount of excess air fed thereto.

References Cited in the file of this patent UNITED STATES PATENTS- Number Name Date 2,389,635 Ramseyer Nov. 27, 1945 2,432,503 Bergstrom et a1. Dec. 16, 1947 2,432,962 Bergstrom Dec. 16, 1947 2,439,730 Happel Apr. 13, 1948 2,532,613 Dutcher Dec. 5, 1950

Claims (1)

1. A PROCESS FOR CRACKING A HEAVY RESIDUAL HYDROCARBON WHICH COMPRISES GRAVITATING A STREAM OF HOT REFRACTORY PEBBLES THROUGH A SERIES OF SEPARATE CONNECTING ZONES COMPRISING A PEBBLE HEATING ZONE; A CRACKING ZONE, AND A PRODUCT QUENCHING ZONE; INTRODUCING A STREAM OF LIQUID HEAVY RESIDUAL HYDROCARBON BOILING AT A TEMPERATURE OF AT LEAST 500* F. TO THE UPPER END OF SAID CRACKING ZONE AND CONTACTING THE HOT PEBBLES IN SAID CRACKING ZONE IN CONCURRENT FLOW SO AS TO RAISE SAME TO CRACKING TEMPERATURE IN THE RANGE OF 1000 TO 1700* F. UNDER CONDITIONS WHICH EFFECT CRACKING OF SAID HYDROCARBON AND DEPOSITION OF COKE ON SAID PEBBLES; WITHDRAWING AN EFFLUENT HYDROCARBON STREAM OF CRACKED PRODUCT FROM AN INTERMEDIATE SECTION OF THE PEBBLE BED IN SAID REACTION ZONE BELOW THE LEVEL OF FEED INTRODUCTION; CONTACTING THE PEBBLE STREAM IN THE LOWER SECTION OF SAID RECATION ZONE WITH A RELATIVELY COOL GAS SO AS TO REDUCE THE TEMPERATURE OF THE OUTGOING PEBBLES TO THE RANGE OF 500 TO 850* F.; TRANSFERRING A FIRST PORTION OF THE PEBBLES FROM THE BOTTOM OF THE REACTION ZONE TO THE TOP OF SAID QUENCHING ZONE; CONTACTING THE PEBBLES IN SAID QUENCHING ZONE IN COUNTERCURRENT FLOW WITH SAID EFFLUENT HYDROCARBON STREAM FROM SAID REACTION ZONE SO AS TO QUENCH SAID PRODUCT STREAM AND DEPOSIT HEAVY TARRY CONSTITUENTS OF SAID STREAM ON SAID PEBBLES IN AN AMOUNT WHICH WHEN BURNED IN SAID PEBBLE HEATING ZONE WITH SAID COKE FURNISHES THE ENTIRE HEAT FOR HEATING SAID PEBBLES; TRANSFERRING PEBBLES FROM THE BOTTOM OF SAID QUENCHING ZONE TO THE TOP OF SAID PEBBLE HEATING ZONE; TRANSFERRING A SECOND PORTION OF SAID PEBBLES FROM THE BOTTOM THE REACTION ZONE DIRECTLY TO SAID PEBBLE HEATING ZONE; BURNING OFF THE TARRY DEPOSIT AND COKE ON THE PEBBLES IN SAID PEBBLE HEATING ZONE WITH A STREAM OF AIR SO AS TO HEAT SAID PEBBLES TO SAID CRACKING TEMPERATURE SOLELY BY THE HEAT OF COMBUSTION OF SAID TARRY DEPOSIT AND COKE; AND RECOVERING THE QUENCHED PRODUCT.

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