US2487743A - Method and apparatus for catalytic conversion of hydrocarbons - Google Patents

Description

Nov 8, 1949 H. n. TRQTTER 2,437,743

METHOD AND APPARATUS FOR CATALYTIC CONVERSION OF HYDROCARBONS Filed Aug. 9, 1946 2 Sheets-Sheet l REGENERATION VENT WASTE HEAT EXCHANGER STEAM DRUM MAKE PUMP DISCHARGE INVENTOR. H. 0. TROTTER ATTORNEYS Nov: 8, 1949 v H. D. TROTTER METHOD AND APPARATUS FOR CATALYTIC CONVERS 16 OF HYDROCARBONS 2 Sheets-Sheet 2 Filed Aug. 9, 1946 FIG. 3

INSULATION STEAM DRUM MAKE PUMP DiSCHAIRGE 1 5/ 1 5 I r x/ 4 7 BOT lOM COLLLCTOR BOX Ill PRE-HEATED FEED T0 STEAM DRUM FIG. 2

INVENTOR. H .D.TROTTER M 2 6/ ATTORNEYS Patented Nov. 8, 1949 METHOD AND APPARATUS FOR CATALYTIC CONVERSION OF HYDROCARBONS Harry Darby Trotter, Kansas City, Kans., assignor to Phillips Petroleum Company,

of Delaware a corporation Application August 9, 1946, Serial No. 689,375

3 Claims.

This invention relates to the catalytic conver sion of hydrocarbons wherein such hydrocarbons are contacted with fixed beds of catalytic material. In a more particular aspect the present invention relates to such a conversion process and apparatus wherein deposition of tar and other high boiling material in equipment associated therewith will be minimized or avoided,

In accordance with existing methods, conversion of hydrocarbons utilizing fixed catalyst beds is carried out by contacting hydrocarbon feed stocks with a suitable catalyst bed or beds, under such conditions that the desired conversion is carried out. Conversion reactions of the type referred to including cracking, polymerization, reforming, aromatization, isomerization, etc. and in particular, reactions in which carbonaceous and heavy molecular weight materials such as tar are formed and carried along with the reaction products. These heavy materials tend to deposit in equipment associated with the conversion system and constitutes an important problem where such deposits tend to restrict flow or affect heat exchange. This problem is particularly acute where the reaction efiluents pass through heat exchangers since these deposits may cause plugging of the exchanger tubes, while the deposition on the interior of the tube markedly decreases the efliciency of the exchanger by decreasing the rate of heat transfer.

Applicant has now discovered a method and apparatus in which deposits of the type described above are avoided by causing the heavy materials in question to be deposited within the bed itself and removed during periodic catalyst reactivation. It is therefore an object of the present invention to provide a method and apparatus for the catalytic conversion of hydrocarbons wherein the carrying out of heavy tar-like carbonaceous material with the products of reaction is minimized or avoided. It is a further object of the present invention to provide a method and apparatus for the catalytic conversion of hydrocarbons wherein the deposition of tar-like material in transfer lines or heat exchanger tubes through which reaction effluents flow, is minimized or avoided.

In accordance with the present invention heavy materials of the type described are condensed within the catalyst bed in the portion of the bed adjacent to the outlet. This condensation is effected by introducing in or near the portion of the bed downstream of the inlet and nearest the reaction chamber outlet, means for cooling said outlet portion of the bed. Such means is preferably a cooling coil through which a cooling fluid is circulated and which will serve to reduce the temperature of that portion of the bed which is adjacent thereto to a point sufficiently low to effect substantial condensation of the undesired tarry material. The cooling fluid utilized for this purpose may advantageously be one which it is desired to heat for some purpose for use in the reaction and/ or reactivation, For example, the cooling fluid may be water or low temperature steam in cases where higher temperature steam is desired for use as a diluent during the conversion reaction or reactivation or both, or for use in purging catalyst before or after reactivation.

The present invention may be described with reference to the attached drawing in which Figure 1 is a flow diagram of a typical fixed bed catalytic cracking system in which superheated steam is formed for use in the process or elsewhere by heat exchange with the effluents of conversion or reactivation in a waste heat exchanger. Figure 2 is a partial vertical cross section of the lower portion of a catalyst chamber showing the cooling coil of the present invention positioned within the bottom portion of the catalyst bed. Figure 3 is a partial horizontal cross section showing the cooling coil disposed in the bottom of the bed. The coil in question is represented only diagrammatically and the length and number of turns thereof will depend entirely on the size of the pipe and the amount of exchange to be effected.

In carrying out the process, oil vapors are passed through a fixed bed catalyst chamber 1 where it is converted by contact at elevated temperatures with a catalyst disposed therein. The products of conversion which contain the unde sired tarry material pass through the bottom por tion of the catalyst bed before leaving the chamber and since this portion of the bed is cooled by coil 2 the high boiling material is deposited on the catalyst within this portion of the bed and also upon the outside walls of the cooling coil. At the lower extremity of the catalyst bed, the conversion products pass through a bottom collector box 5 which is a catalyst-retaining assembly, conventionally inserted below the catalyst bed to support and retain the catalyst and to collect any catalyst fines which may be present or formed during the use of the catalyst and which tend to be removed with the hydrocarbon products; it is usually covered by screens and generally contains several layers of various sized pellets or lumps of inert material which act as a filtering medium. The products then flow through waste heat exchanger 3. During the conversion reaction, valves B and D are closed and valves A and C are open. Water is introduced Via line 4 through valve A into cooling coil 2 and the resultant steam flows into steam drum 1 through valve C and line 6. During the reactivation valves A and C are closed and valves B and D are opened and the coil is vented to the atmosphere. During reactivation the temperature of the catalyst above and below the coil will be relatively the same. During reactivation water flows into steam drum land thence through -line 8 into waste heat exchanger-3 whereit is converted to steam by heat exchange, the

steam flowing to drum 1 via line 9. During the B may be operated by a level control on steam-x drum 1 (not shown) to maintain level in the steam drum and to allow a desired amount of water to flow during conversion.

Following the conversion, the catalyst. bed is purged of residual hydrocarbon material by introducing a diluent such as steam at the inlet to the catalyst chamber and after a short purging period is ready for reactivation. Carbonaceou-smaterial deposited on the catalyst-as a result'of the con version is. removed by introducing an'oxygen-com taining gas under combustion conditions atthe inlet to the chamber. During the reactivation, a zone of combustion tends to move from the inlet to the outlet of the catalyst chamber and thehigh molecular hydrocarbons or tars which have been deposited down stream of the chamber are removed from the lower portion of the bed by combustion.

The coil 2 is preferably constructed of an alloy material which will withstand reaction and reactivation temperatures. The coil is designed to give a surface large enough to effect the desired extent of cooling. In general, a decrease in temperature in the bottom catalyst zone, or the hydrocarbon outlet temperature, of fromlOO-SOO" F.

below the conversion temperaturewill be sufiicient to condense a substantial proportion ofhydrocarbons boiling above about '700-900 F. The surface area, and hence the cooling capacity of the coil, is controlled by varying thenumber of turns and the diameter of the pipe.

Example vI A catalyst chamber has positioned therein a bed of bauxite cracking catalyst 13 ft. high and 10 ft. in diameter. The bed contains 30 tons of 4-8 mesh bauxite. A cooling coil is-positionedin the downstream end of the bed and is located intermediate the lower quarter thereof. The coil isof 3 inch extra strong steel pipehaving 1.091 square feet of external surface per linear foot. The total surface area ofthe coil is 840 squarefe'et: During the process portion of the cycle 250 barrels per hour of 36 A. P. I. virgin gas oil froni-We'zst-'-Iexas crude is'charged. The conditions with and without the cooling coil functioning as described above are as follows:

Under the foregoing conditions,- substantially no condensation of high boiling material took 7 place in the absence of cooling by means of the coil, but with the coil in use approximately 2.5% by weight of charge, of high boiling carbonaceous material boiling over about 900-F., is condensed or deposited in the bednear the chamber outlet;

This deposit is removed when the catalyst is reactivated .by oombustionwith oxygen-containing gas. When the 'coil was not in use substantial carbonization and coking of the waste heat exchanger tubes was noted with resultant poor flow and heat transfer.

In general, catalytic cracking of gas oil or other petroleum hydrocarbons may be effected in vapor phase at temperatures in the range of 850-l150 using bauxite, silica alumina, acid treated clay, or other well known catalysts. Dehydrogenation'and other conversion reactions are carried out in the vapor phase under conditions well known to the art, and in each case, deposition of high boiling material in'the cooler portion of the catalyst bed will increase efiicien'cyof the heat exchangers or other equipment connected to the reaction chamber outlet. Temperatures in the coolportion of the bed are maintained sufficiently low to insure deposition of a substantial proportion of higher boiling material in the bed.

I claim:

1. In the catalytic conversion of hydrocarbons by contact with a fixed bed ofcatalyst-unde'r conversion conditions wherein high boiling carbonaceous materials are obtained-along with other conversion products and wherein such materials .end to deposit externally of the conversion zone, the method which comprises cooling a lowermost portion of the catalyst bed near the conversion zone outlet to a temperature low enough to cause condensation and adsorption of undesiredhigh boiling carbonaceous material on said cooled portion of said catalyst bed, retaining said condensed high boiling material adsorbed on'said lowermost portion of the catalyst bed during the conversion of hydrocarbons, and removing said condensed and adsorbed material duringsubsequent catalyst reactivation.

2.-A process for catalytically cracking hydrocarbon oils which comprises flowing-said oilsin vapor phase through a cracking catalyst disposed in a fixed bed at cracking temperatures','cooling the downstream portion ture of about 100 to 500 F. below thecracking temperature in the upstream portion of the .bed, condensing and adsorbing in said cooled portion of the bed high boiling carbonaceousmaterial; and

removing said condensed material by combustion following the cracking step.

3. A process for catalytically cracking hydrocarbon oils which comprises fiowingsaid'oilsin vapor phase through a cracking catalyst disposed in a fixed bed at cracking temperatures, cooling the downstream portion of the bed to a temperature substantially below the'cracki ng temperature in the upstream portions of the bed, thereby condensing and adsorbing in said cooled portion of the bed-high boiling-carbonaceous material, retaining said condensed high boiling-material adsorbed on said downstream portionof thecata lyst bed during the cracking of said oils'pandremoving said condensed material by combustion following the cracking step.

HARRY DARBY TROTTERI REFERENCES. CITED The following references are .of record in the file of this patent:

UNITED STATES lPJYI'ENI-S of the bed-toa tempera-

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