US2736686A - Pebble heater reactor employed in the conversion of hydrocarbons, with the use of inert solids - Google Patents

Description

Feb. 28, 1956 L. J. WEBER PEBELE HEATER EEAOTOE EMPLOYED 1N THE CONVERSION OF HYDROCARBONS, WITH THE USE OF INERT SOLIDS Filed June l2, 1950 EFFLUENT 34 r T f PEBELE 2S` i HEATER .y 2e 1 i I EFFLUENT l 6 33 *22 i REACTION r4 CHAMBER la lo l 0 i la FEED 24 STEAM U 24 STEAM FEED!8 I7 32 I 2 24 3| STEAM STEAM INVENTOR. L. J. WEBER A T TORNE KS' United States Patent O PEBBLE HEATER REACTR EMPLOYED .IN THE 'CONVERSION GF HYDRGCARBONS, WITH THE USE OF INERT SOLIDS 'Louis J. Weber, Bartlesville, 0kla., assigner to Phillips Petroleum Company, a corporation of Delaware Application June 12, 1950, Serial No. 167,542

7 Claims. (Cl. 196-55) This invention relates to thermal conversion of hydrocarbons in a pebble lheater and to apparatus for effecting this type of process. One aspect of the invention lpertains to the thermal cracking and conversion of vheavy oils to 'lighter hydrocarbons.

vPebble heater apparatus is finding increasing favor -in the conversion of hydrocarbons at elevated temperatures in the range of 1500 to about 2500 F. because of the fast heating rate and other process advantages provided by the pebble heater. A conventional pebble heater utilize/s a pebble heating chamber having `means for passing .hot combustion gas upwardly through a gravitating mass :of refractory pebbles which are heated therein before de- .scending through an axially positioned throat to a reaction chamber of similar shape and construction to the pebble heating chamber. The pebbles are contacted in the conversion zone or chamber with a countercurrent stream of ihe hydrocarbon to be reacted or converted so as to ,heat the same to reaction temperature and supply the .heat of 4reaction required to effect the conversion. The 4pebbles then gravitate from the lower end of the reactor to the bottom of an elevator which lifts them to a point -above .the top of the pebble heater chamber from whence they gravitate to that chamber for reheating and 4gravitation to lthe reaction chamber. The system from the pebble inlet in 'the heating chamber to a pebble feeder device in the .conduit between the bottom of the reaction chamber and the lower end of the elevator is maintained full of a compact gravitating mass of pebbles at all times during operation of the unit.

The heating and reaction chambers of conventional pebble heater apparatus are usually cylindrical vin yshape with a lshort conical top and conical bottom and since the main section of the chamber is cylindrical, substantially uniform pebble and gas ow are effected in that part of the chambers. Uniform pebble and gas iiow are highly desirable in gas heating and chemical reaction processes where uniform heating rates are desirable. In the endothermic conversion of hydrocarbons it is desirable to -raise the temperature of the hydrocarbon feed extremely rapidly through the temperature range just below reaction temperature and to quickly react the hydrocarbon so as to avoid undesirable side reactions which decrease the yield of the desired product and contribute to the inefciency of the particular process being effected.

In pebble heater processes it is highly desirable from the standpoint of efficiency and economics to extract as much heat as possible in the reaction chamber so as to reduce the temperature thereof suiiiciently to render it 'feasible to transfer the pebbles in elevator equipment constructed from ordinary cast iron and other relatively low temperature metals without resorting to expensive alloys required for higher temperatures.

It is a primary object of the present invention to provide an improved process for the thermal conversion of hydrocarbons in a pebble heater. Another object of the invention is to increase the rate of heating ,hydrocarbons xat'temperatures just below their reaction temperature and ICC to effect their rapid reaction and conversion so as to avoid deleterious side reactions. It is also an object of the invention to provide a hydrocarbon conversion process in a pebble heater which increases the contact time in the feed preheating stage of the process. Another object is to effect more eicient heat-exchange in a pebble lheater in hydrocarbon conversion processes. A further object of the invention is to provide an improved pebble heater reactor. Other objects of the invention will become apparent from a consideration of the accompanying disclosure.

The invention is primarily concerned with the rate oi' pebble and gas iiow in a pebble heater reaction chamber. In order to provide for longer contact time between the hydrocarbon feed and the gravitating pebbles in the feed preheating stage and sharper heating of the hydrocarbon and more rapid reaction in the upper section of the reactor, the invention provides a conical section in the reaction chamber to which the vhydrocarbon feed is intro duced at the bottom over the entire cross-sectional area and passes upwardly vtherethrough at progressively increasing ow rates so that the highest flow rate and `most rapid heat-exchange and therefore hydrocarbon heating and reaction is effected in fthe Vupper section of the reactor. This apparatus and method of operation permit the withdrawal of the reaction products Jmore rapidly than is pro- 'videdby conventional apparatus and processes. The con- IVical shaped reaction chamber vof the invention also permits longer feed-pebble contact time iin `the lower rsection of the reaction chamber so as to increase the Aheating eic'iency and effect a lower pebble exit temperature from 'the reaction chamber.

A more complete understanding of the invention may 'be had from a consideration of the accompanying drawing of which Figure l is a diagrammatic illustration 'of a yer-tical section of one modification of the apparatus of the invention; Figure 2 is a similar -type of showing of another modification of 'the pebble reactor of the invention, and 'Figure 3 is a plan view or elevation of the `principal elements of a pebble heater apparatus.

Referring to Figure l, reactor 10 `has a top conical section 11 and a bottom conical section 1'2. The reactor comprises a'metal shell 13, a refractory 'lining 14 capable of withstanding moderately high temperatures, and 4an yinner Vlining 15 consisting of "high tempera-ture refractories withstanding temperatures up to the region of 3560" 'F. Pebbles are introduced to the reactor through a throat or inlet section 16 and are Withdrawn vthrough conduit 17 at the bottom of conical section l2. Hydrocarbon feed is intrduced to the reaction zone at lthe approximate level of the lower end of conical section 11 by means of inlet line 18 which communicates with distribution spider 19 comprising perforate spokes or feeders 21. tEtiiuent line 22 communicates with the gas space 23 formed fin the upper part of the reactor by the extension of the lining of throat 16 into the reactor. .Steam lines 24 communicate with the bottom of the reactor for .the purpose of admitting steam thereto in certain types of processes which are discussed hereinafter.

It should be understood that other types of gas .distribution elements which function yto distribute the hydrocarbon feed uniformly over a 'horizontal -cross-section of the reaction chamber may be utilized 'in the apparatus and process. The extension of the throat lining into `the reactor and the design of the upper section ofthe reactor around the effluent line maybe controlled so as to provide the most suitable vapor collecting space for the particular reaction to be effected in the apparatus.

Figure 2 illustrates a modification of the apparatus having a plurality of effluent lines and pebble vliow control means to permit a flatter conical bottom section than would be otherwise desirable vfrom .the standpoint of tuniformity of pebble ow. The parts or elements of Figure 2 have the same reference numerals as the corresponding parts or elements of Figure l. Flow control member 30, which may comprise a metal plate having concentrically arranged holes distributed thereover for downward flow of pebbles therethrough or a series of concentric annular members providing annular pebble passageways, is de signed to effect uniform pebble ilow over the horizontal cross-section of the reactor at this point so as to permit the utilization of a considerably flatter bottom than is shown in either Figure 1 or 2. The apparatus of Figure 2 also provides a longer cylindrical section which serves to increase carbonization and vaporization period when cracking heavy stock.

The apparatus of Figure 3 comprises reaction chamber 10, a superposed pebble heating chamber 25 connected thereto by throat 16, and a pebble elevator 33 which may be of the bucket, screw, or gas lift type communicating at its upper end through conduit 34 and pebble inlet 28 with heater 25 and at its lower end, through conduits 17 and 31, with the bottom of the reactor. A fuel-air mixture or hot combustion gas is fed into the bottom o-f heater 25 by means of line 26 and hot combustion gas passes upwardly through the heater and egresses through stack 27. Hydrocarbon feed is introduced to the reactor through line 18, is heated as it ascends the pebble bed therein, and the effluent is passed through line 22 to suitable separation and recovery means, not shown, but well known in the art. In operation of the unit, pebble feeder 32, which may be a table-type or other conventional feeder, controls the flow of pebbles through the system and is operated so as to maintain the chambers and conduits filled with pebbles at least up to pebble inlet 28 in heater 25. Operating in 'this manner is essential in order to take advantage of full capacity of the unit, minimize mechanical shock to the pebbles, and maintain gas ow between the heater 25 and reactor 10 at a minimum. In some installations it is desirable to introduce steam or other non-deleterious gas as a blocking gas to throat 16 and also conduits 17 and 28.

The process and apparatus of the invention are designed for the endothermic conversion of hydrocarbons broadly, but have particular utility in conversions, involving cracking, of such feed stocks as gas oils, fuel oils, reduced crudes, and heavy residuums. In these applications of the process, the feed stock is at least partially vaporized in the lower section of the reaction zone which may be considered for practical purposes the area just above feed distributor 19. The vapors thus produced pass upwardly through the gravitating pebble bed at pror gressively increasing velocity. As the vapors pass upwardly, they contact pebbles which are progressively hotter as the top of the chamber is approached and thus the vapors may be cracked for the production of oleiins, such as ethylene, for example, under optimum conditions of temperature and residence time. Suitable temperature is usually in the range of about 1300 to l900 F., but in some cases may be as high as 2500 F., and the residence time is desirably in the range of 0.5 second to .001 second for optimum yields. When it is desired to produce acetylene by the cracking of the vaporized portion of the feed, it is preferred that the temperature limit be raised to about 2500 F. with short residence times in the order of .001 to .0001 of a second.

The unvaporized portion of the feed stock passes downwardly from the point at Which feed is introduced concurrently with the pebbles. In the lower portion of the reaction zone the rate of both hydrocarbon and pebble flow are the lowest in the reactor and because of this fact the unvaporized portion of the feed is converted to coke or carbon which adheres to the pebbles. Satisfactory coking requires a residence time in the range of to 30 seconds and a temperature in the range of 1000 to 1500 F., which conditions are readily provided by the design and operation of the apparatus described. In this coking operation it is quite essential that a relatively dry coke be produced to avoid balling or agglomeration of the pebbles. Producing dry coke ordinarily requires long residence times which may approach the time of 15 to 30 minutes. The necessary residence time can be reduced by introducing steam through lines 24 to the bottom section of the reaction chamber in order to strip, dry, or distill the coke and avoid agglomeration of the pebbles. Since the presence of steam in the cracking zone is advantageous in hydrocarbon cracking processes, the i11- troduction of steam into the bottom section of the reactor for the purpose of hastening the coking process and producing dry non-agglomerated coke enhances the whole operation.

It is also frequently desirable to admit or introduce steam with a feed stock to improve the vaporization as well as the subsequent cracking of the vaporized portion. Light hydrocarbons, such as propane, may also be advantageously admixed with the feed to accomplish this purpose.

The following data illustrates the utilization of the invention in cracking a heavy residuum of 16 A. P. I. gravity in apparatus designed in accordance with that shown in the drawing.

Flow rates in pounds per hour:

As compared with the cracking of the same feed in a conventional pebble heater reactor of cylindrical design under conditions which are otherwise comparable, the production of gasoline (C5-400 F.) is increased 2.6 weight per cent, while the yield of product boiling in the ranges G-750 F., 750-900 F., and above 900 F. are each decreased approximately 0.1 weight per cent. The coke .deposit in the process of the invention is 0.2 weight per cent less. Another important advantage of the process lies in the fact that the butanes and lighter product is decreased 2.1 weight per cent and in this fraction the increase in ethylene is from 14.1 per cent to 16.1 per cent or an increase in ethylene production of 2 per cent. (All per cents are based upon the weight of the feed.)

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 normally liquid hydrocarbon which comprises gravitating a hot compact stream of refractory pebbles at a temperature above the cracking ltemperature of said hydrocarbon to a cracking zone of uniformly increasing horizontal cross-sectional area in the direction of pebble ow, maintaining a compact gravitating bed of said pebbles in said reaction zone; introducing a stream of said hydrocarbon in liquid form to the lower portion of said bed of pebbles under conditions so as to vaporize a substantial portion of said hydrocarbon',

passing the Vaporized hydrocarbon upwardly through said reaction zone at a uniformly increasing ow rate and a contact time in the range of 0.5 to 0.0001 second so as to crack the same to lighter hydrocarbons; transferring pebbles from the bottom of said cracking zone to a heating zone above said cracking zone; contacting the pebbles in said heating zone with a stream of hot combustion gas so as to heat same to a temperature above said cracking temperature; gravitating the reheated pebbles to said cracking zone; coking the unvaporized portion of said hydrocarbon on the pebbles in the lower portion of said zone; and recovering an effluent from said cracking zone.

2. The process of claim 1 in which the coke-bearing pebbles are contacted in said heating zone with an oxygencontaining gas so as to burn 0E said coke.

3. A process for cracking a hydrocarbon material which comprises heating a gravitating compact stream of refractory pebbles in a heating zone to a temperature at least 150 F. above a predetermined cracking temperature in the range of 1300 to 2500 F. but below the softening point of said pebbles; gravitating the resulting hot pebbles in a compact stream through a gradually and uniformly diverging reaction zone so that the rate of pebble flow is gradually and uniformly retarded through the entire reaction zone; passing a fluid stream of hydrocarbon material upwardly through said reaction zone in direct contact with said pebbles at progressively increasing flow rates effected by the convergence of said reaction zone so as to heat ysaid hydrocarbon material to said predetermined cracking temperature and effect cracking thereof whereby the retarded pebble and fluid flow in the lower section of said reaction zone cooperate to effect maximum heatexchange and pebble exit temperature below 800 F. and more rapid pebble and uid flow in the upper section of said reaction zone so as to effect sharper heating and shorter contact time than in a reaction zone of uniform cross section; transferring pebbles from the bottom of said reaction zone to said heating zone; and recovering cracked hydrocarbon from said reaction zone.

4. In a hydrocarbon conversion process wherein a convertible hydrocarbon stream is contacted in countercurreut ow with a gravitating compact bed of hot inert, refractory, heat-transfer, pebbles so as to heat and convert said hydrocarbon, the lower section of said bed functioning as a feed preheating section and the upper portion thereof functioning as a reaction section, the improvement comprising maintaining said bed in the form of a cone -so as to gradually and uniformly decrease the pebble flow rate therein in the direction of ow and also increase the hydrocarbon flow rate in its direction of flow thereby providing longer contact time in the lower preheating section of the bed and shorter contact time and faster heating in the reaction section of the bed thereby preserving hydrocarbon products which would otherwise be destroyed.

5. A process for eiecting an endothermic chemical reaction which is enhanced by sharp heating and short reaction time, which comprises gravitating a compact mass of refractory pebbles through a pebble heating zone in Contact with a stream of hot combustion gas so as to heat said pebbles to a temperature above the temperature of said reaction; gravitating the resulting hot pebbles in a compact uniformly diverging ystream through a reaction zone below said heating zone in contact with a countercurrent, uniformly converging stream of fluid reactant so as to effect a relatively long contact time in the lower portion of said reaction zone and a relatively short reaction time in the upper portion thereof; recovering an effluent from said reaction zone as the product of the process; and recycling pebbles from the bottom of said reaction zone to the top of said pebble heating zone.

6. The process of claim 3 in which the cracking temperature in the upper section of the reaction zone i-s maintained in the upper portion of the temperature range and the reaction time is maintained in the range of 0.001 to 0.0001 second so as to produce a substantial amount ot acetylene.

7. In combination with an upper pebble heating chamber and a connecting throat, a pebble heater reactor comprising an upright closed refractory-lined vessel having a top conical section and an inverted conical bottom section; a pebble inlet at the apex of said top conical section connecting with said throat; a pebble outlet at the apex of said conical bottom section; uid distribution means extending across said vessel at the bottom of said top section; a feed line connecting to said distribution means; a gas outlet in the upper portion of said top conical section; and a compact bed of spherical, refractory, heatexchange pebbles extending from a pebble inlet in said pebble heating chamber to `said pebble outlet.

References Cited in the le of this patent UNITED STATES PATENTS 1,174,464 Agnew Mar. 7, 1916 2,389,636 Ramseyer Nov. 27, 1945 2,406,810 Day Sept. 3, 1946 2,561,996 Robinson July 24, 1951

Claims (1)

1. A PROCESS FOR CRACKING NORMALLY LIQUID HYDROCARBON WHICH COMPRISES GRAVITATING A HOT COMPACT STREAM OF REFRACTORY PEBBLES AT A TEMPERATURE ABOVE THE CRACKING TEMPERATURE OF SAID HYDROCARBON TO A CRACKING ZONE OF UNIFORMLY INCREASING HORIZONTAL CROSS-SECTIONAL AREA IN THE DIRECTION OF PEBBLE FLOW; MAINTAINING A COMPACT GRAVITING BED OF SAID PEBBLES IN SAID REACTION ZONE; INTRODUCING A STREAM OF SAID HYDROCABON IN LIQUID FORM TO THE LOWER PORTION OF SAID BED OF PEBBLES UNDER CONDITIONS SO AS TO VAPORIZE A SUBSTANTIAL PORTION OF SAID HYDROCARBON; PASSING THE VAPORIZED HYDROCARBON UPWARDLY THROUGH SAID REACTION ZONE AT A UNIFORMLY INCREASING FLOW RATE AND A CONTACT TIME IN THE RANGE OF 0.5 TO 0.0001 SECOND SO AS TO CRACK THE SAME TO LIGHTER HYDROCARBONS; TRANSFERRING PEBBLES FROM THE BOTTOM OF SAID CRACKING ZONE TO A HEATING ZONE ABOVE SAID CRACKING ZONE; CONTACTING THE PEBBLES IN SAID HEATING ZONE WITH A STREAM OF HOT COMBUSTION GAS SO AS TO HEAT SAME TO A TEMPERATURE ABOVE SAID CRACKING TEMPERATURE; GRAVITATING THE REHEATED PEBBLES TO SAID CRACKING ZONE; COKING THE UNVAPORIZED PORTION OF SAID HYDROCARBON ON THE PEBBLES IN THE LOWER PORTION OF SAID ZONE, AND RECOVERING AN EFFLUENT FROM SAID CRACKING ZONE.

Images