US2091375A - Treatment of hydrocarbon oils - Google Patents

Description

Aug. 31, 1937. YZEL 2,091,375

TREATMENT OF HYDROCARBQN OILS Filed Feb. 29, 1936 3 Sheets-Sh 1 lOl I02 FIG. 2

FRACTIONATOR 1 39 HEAT EXCHANGER ABSORBER FURNACE 6'7 RECEIVER M.

ENVENTOR Aug. 31, 1937. R. PYZEL TREATMENT OF HYDROCARBON OILS 3 Sheets-Sheet 3 Filed Feb. 29, 1936 INVENTOR ROBERT PYZEL MILE A m H L UQMRNQ NWW NN H H D I BY TORNEY Patented Aug. 31, 193'! UNITED STATES PATENT OFFICE Robert Pyzcl, Chicago, Ill., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application February 29, 1936, Serial No. 66,320

3 Claims.

This invention relates particularly to the treatment of lower boiling dlstillates produced in the refining of petroleum such as kerosene, naphtha or gas oil fractions produced either in the primary 5 non-cracking distillation of crude petroleums or incidental to cracking processes.

In a more specific sense, the invention is concerned with the pyrolytic decomposition of such distillates under particular conditions of operal0 tion which have been found to yield large quantitles of unsaturated or olefinic hydrocarbons, both gaseous and liquid; the liquid hydrocarbons boiling within the range of commercial gasoline say up to 400 F. being of superior antiknock value.

The present process is readily distinguishable from commonly employed pyrolytic or cracking processes in the employment of somewhat higher temperatures, considerably lower pressures, and much shorter time factors. In ordinary cracking processes conducted upon petroleum fractions of both a distillate and residual character for the, production of maximum yields of gasoline, it is currentpractice to employ temperatures within the approximate range of 850 to 1000 F., pressures from 100 to 1000 pounds per square inch above atmospheric and a long time factor, the last resulting from the employment of cracking coils of considerable length and/or large vaporizing or reaction chambers following the heating elements. Such conditions of operation are generally conducive to the formation of large yields of low boiling liquid hydrocarbons of a character suitable for use as motor fuel, since due to the long time factor an equilibrium is approached corresponding to the temperature and pressure employed and a certain amount of secondary polymerization and condensation reactions take place following the primary reactions of decomposition.

In contradistinction to these conditions of operation the present process limits the decomposition reactions substantially to the primary reactions of decomposition so that equilibria corresponding to the temperatures and pressures as ordinarily employed are not reached, and the secondary polymerization reactions are obviated.

In one specific embodiment, the invention comprises vaporizing liquid hydrocarbon oil mixtures without substantial decomposition thereof and subjecting the vapors to pyrolysis at temperatures of from approximately 1500 to 1700 F. under subatmospheric pressures and for times less than 0.05 second.

It will be obvious to those skilled in the art of cracking hydrocarbons to produce lower boiling products that the present process may be conducted in various types of apparatus in which the various inter-connected elements are suitably proportioned to take care of charging stocks of somewhat varying character, along with different rates of flow and extent of cracking. Without unduly limiting the scope of the invention, the operation of the process will be described in connection with a particular type of apparatus which has been found to give satisfactory operation and good yields of desired products. To assist in this description the attached drawings have been provided, Fig. 1 of which shows partly in side elevation and partly in section, a general arrangement of an apparatus which may be used, while Fig. 2 is a cross sectional plan view of a portion of the apparatus taken along a plane indicated by the line 2-2 in Fig. 1. Fig. 2 merely indicates one arrangement and type of refractory filler which may be used for accomplishing the operation at the desired low time factors. Fig. 3 which I includes graphs A, B, C, D, E and F shows by means of curves and shaded sections the temperature conditions obtaining in pieces of filling material at different stages of operation. In these figures the vertical coordinate is the temperature, which, however, is not shown as an exact scale but only schematically. Fig. 4 is a representation by means of a legended chart of the multiple furnace type of operation which superimposes the periods and the cycle of operations to show that continuous operations may be conducted with a minimum of manipulation. Figs. 3 and 4 will be used in a separate portion of the description which will follow the description of a single furnace operation given inconnection with Figs. 1 and 2.

Referring to Fig. 1 of the drawings the principal units of the plant are seen to be a vaporizing element 9 and a cracking element 13 followed by suitable equipment for fractionating and recovering the products, utilizing the heat of the cracked vapors to preheat charging oil and an absorption plant to insure effective recovery of liquefiable vapors from fixedgases. Cracking element I3 is of special design and construction to make possible the use of relatively high temperatures for comparatively brief time intervals and will be later described in more complete detail.

In the operation of the process, a charging stock such as gas oil or kerosene distillate, for example, is admitted to the plant by way of charging line I and valve 2, to pump 3 and discharged therefrom byway of line l and valve 5 through a heat exchanger I. While the pressure in, the vaporizer, the main cracking element, and a portion of the subsequent cracking equipment is less than atmospheric, it is usually better to 5 maintain some pressure on the charging oil during its passage through the heat exchanger to lessen the possibility of leaks. This may be accomplished by suitable manipulation of control valve 8 in raw oil discharge line I from the heat 10 exchanger which leads to the vaporizing element 9 suitably disposed in a furnace setting Ill. The i vaporizing element may conveniently be a multiplicity of serially connected tubes or any other conventional form of heater commonly employed in refining processes.

The temperature and absolute pressure of the heated vapors which leave coil 9 by way of line II and valve I2, are preferably about 900 F. and 100 to 200 millimeters of. mercury, respectively.

Cracking element I 3 is essentially a regenerative type furnace containing refractory filling material (such as carborundum forms, for example, or other material capable of withstanding high temperatures) which is alternately heated to a suitable temperature and then employed to impart sufficient heat to the oil vapors supplied to their zone to effect the desired pyrolysis thereof. In the drawings I5 and I 6 indicate sections of the heater filled with special refractory forms heated by surface combustion during the heating period. A sectional plan view of this portion of the furnace is illustrated in Fig. 2. Sections II and I1 indicate extra sections .of refractory material, preferably in lattice arrangement, which store additional heat recovered from the combustion gases produced in sections I5 and I6. The portion of. the furnace indicated at I8, I9 and 20 represent intervening free spaces. Depending upon the time factor found best in different cases, one or any desired number of the surface-combustion sections I5 and I0 or the refractory filler sections I1 and It may be employed. Where very short time factors of the order of 0.005 sec. are used, a single-surface combustion section may be sufficient.

Referring to Fig. 2, which represents a section of the combustion zones I5 and I8, a pre-formed mixture of combustible gas and air is admitted through lines IN on opposite sides of the furnace and the mixture first enters distributor spaces I02, flowing thence through openings I03 which pass through the center of the forms. These forms are spaced a definite distance apart by lugs I04 and contain perforations I05 through which the pre-formed combustion mixture passes to burn in spaces I06 between the forms. By proper regulation of the proportion of fuel to air, and proper proportioning of the size and number of perforations I05, combustion is controlled to take place on the surface of the forms within spaces I06 without deposition of carbon, the forms being thereby heated to the high temperature required for the subsequent cracking of admitted ,oil vapors which are passed through the spaces I 06 under a predetermined time condition. The use of relatively large forms as filler in regenerative furnaces with resultant higher heat capacity makes possible a considerable extension of the cracking period since as will be later more fully disclosed it is possible to alternate the cracking of the oil vapors with idling periods which permit the flow of interior heat to the surface of the'forms so that they are again at a sufiiciently high temperature to effect the desired type of cracking.

When heating the refractories to store heat necessary for cracking oil vapors, the resulting combustion gases may, if desired, be caused to pass both ways out of the cracking section, that is, some may be released upwardly through line 30 and valve 3i and the remainder downwardly through line 32 and valve 33. In the drawings line 22 is a header for gaseous fuel (such as for example the fixed gases from the process) and valves 23' and 25' in lines 23 and 24 control the admission of regulated amounts of gas to combustion zones I5 and I6 as desired. Line 26 is for the admission of controlled amounts of air to the gas lines so that the preferred pre-formed combustible mixture .of air and gaseous fuel is admitted to the combustion spaces to insure the surface combustion on the filling material. Valves 21, 28, and 29 are provided to permit control over the quantity of air admitted at various points. This type of combustion provides a high temperature and a uniform distribution of heat so that there are no large temperature gradients in the sections of filling material. Furthermore, the combustion may be controlled so that any carbon or carbonaceous residue left on the refractory filler from the cracking step is burned off, leaving a ,clean surface for the cracking operation. To further assist in the heating period, and particularly in bringing the furnace up to a temperature sufficient for instigating surface combustion, ordinary combustion gases, such as, for example, those from the vaporizing furnace I0, may be admitted to the cracking furnace by way of line 30 containing valve 3| to flow downwardly therethrough. Valves 3i in line 30 and 33 in line 32 are ordinarily of. high temperature-resistant material and/or special construction to insure their tightness since they are exposed to relatively high temperatures during the combustion periods and must allow no leakage of air or other gases into the furnace during the cracking period. When the flow through the cracking element is reversed upon the admission of oil vapors, valve 3i may be opened until residual products of combustion from the heating period are swept out, to avoid dilution of the cracked vapors with these gases in subsequent portions of equipment. I

The cracking zone is; preferably enclosed in a jacket 2| of high temperature metallic alloy or the like, which in turn is surrounded by heavy insulating or lagging 2|.

In the furnace, as shown, vaporized oil is ad mitted from line II through valve I2 and passes upwardly through heated refractory sections I4, I5, I6 and I1 leaving the cracking zone through line 34 containing control valve 35. In the case of gas oil and kerosene distillates boiling in the approximate range of 400-750 F., satisfactory results in respect to olefin production have been obtained using temperatures of from 1500-1700 F. for relatively short times. To successfully eliminate secondary polymerization reactions among the cracked products, it is desirable to quickly cool or "quench them, and this may be accomplished, for example, by admitting any one or more of several of the intermediate and final products of the process to line 34 by way of line 9| containing control valve 92. The particular quenching media and the details of their production and recirculation will be taken up in proper sequence. The temperature is preferably reduced to some point below'1000 F. before the cracked products enter heat exchanger 6. It is to be understood that a plurality oi cracking units such as the regenerative type described may be alternately operated and heated preparatory to further operation although only one such unit is shown in the drawings. Such operation is generally imperative if the process is to be made continuous, since normally the alternate blasting and cracking cycles are relatively short and the stream of oil vapors to be cracked must be frequently diverted to freshly heated units. In some units of this character the time of blasting. is approximately 5 minutes, while the time that the heated filling material may be used to crack entering oil vapors is of the order of 3 minutes. Such short times are usually necessitated by the fact that best results are obtained only when there is a fairly accurate control of both temperature and time of exposure thereto. Obviously, mechanical controls may be provided which shift the necessary valve settings on a time basis to reverse the flow through the cracking units. Devices of this character are fairly well known in the cracking art, and since they constitute no special feature of the present invention, they are not illustrated or described in detail.

The cracked products supplied to heat exchanger 6 serve to preheat the charging stock for the process by indirect heat exchange therewith in this zone, as previously mentioned, following which the partially cooled products pass through line 36 and valve 31, to a primary separator or fractionator 38, which is provided to permit dropping out any heavy tarry material which is withdrawn through line l8 and valve 81 to a pump 88 which discharges through line 09 and thence either through line '9' and valve 90' to quenching line Si or through valve in line 89 to cooling and storage or elsewhere as desired. The amount of residual tar used at this point for quenching will be inversely proportional to its coking tendencies.

The vapors and fixed gases from separator 38 pass through line 38 containing control valve 40 and enter a more eflicient fractionator 4|, which is of suitable design and capacity for production of an overhead comprising only gasoline boiling' range constituents, while leaving heavier intermediate products as a bottom reflux which may be recycled alongwith the fresh feed for further conversion or used as quenching material. Thus the bottom refiuxes from Iractionator 4| are withdrawn through line 93 containing control valve 94 and pumped by pump 95 which discharges through line 96 containing control valve 91 either to quenching line Si by way of line 96 containing control valve 91" or to raw oil line I by way of branch line 96' containing control valve 91'.

Vapors and fixed gases pass through overhead vapor line 42 containing control valve 43, through condenser 44 (which may be operated at lower than atmospheric temperature) and then through rundown line 45 containing control valve 48 to receiver 41. I The liquid accumulating at this point, while preferably containing no constituents boiling higher than the end pointof ordinary gasoline, may yet not contain certain of the lighter ends of the liquid products since the plant is still under vacuum up to this point. The complete recovery of the vapors of non-liquid products is accomplished in the subsequent absorption plant to be presently described. Liquid products are removed by way of line 48 containing control valve 49 to pump 50 which discharges through line 5| containing control valve 52 to-the top of the fractionator to control the boiling range of eiiluent vapors or through branch line 53 containing control valve 54 to ultimate storage, where it is mixed with further recovered liquid material from receiver 16.

To recover normally liquid products, use is made of the ordinary cyclic absorption plant hook-up. Thus the gas from receiver 41 which may be quite rich in gasoline vapors passes through line 55 containing control valve 56 to pump 51 which discharges through line SI containing control valve 59 and admits the gas-vapor mixture under a moderate superatmospheric, pressure to the bottom portion of an absorption tower O0 to pass upwardly therethrough counter-current to a descending flow of absorber oil. The fixed gases at this point pass through line OI containing control valve 99 to a pump'llili which discharges the gases either into quenching line 9| through valve 92" or to storage through line 9| containing control valve 92'.

The absorber oil containing liquid gasoline fractions and some dissolved gases passes through line 6| containing control valve 62 to pump N which discharges through line 64 containing control valve through a heating element 66 disposed to receive heat from a furnace 61, so that the temperature of the mixture may be, raised sufliciently to volatilize absorbed hydrocarbons, the heated materials passing through line 68 containing control valve 89 to fractionator I0, which permits the vaporization and fractionation and ultimate recovery of the gasoline constituents and dissolved hydrocarbon gases. The overhead vapors from fractionator 10 pass through vapor line H containing control valve 12 and the liqueflable constituents are condensed during passage through condenser 13 to flow along with uncondensed gases through rundown line 14 containing control valve 15 to a final receiver 16 having a fixed gas release line 11 containing control valve. I8 and liquid draw line 19 containing control valve 40.

from line 9i, and the liquids are preferably blended with those from line 53. 1

The absorber oll,stripped of its light constituents, then passes through line it containing control valve 82 to recirculating pump 83 which discharges the oil (with cooling ,if necessary) through line '4 containing control valve 5 back to the top of absorbing tower 80 to repeat its cycle. Line II containing control valve 82' is indicated for the;admission of absorbent either originally or for makeup purposes.

The foregoing description will indicate in a general way the type of cracking process comprised within the scope of the present invention. However, from a practical standpoint, it is imperative that operations be made continuous and that the shifting from heating to cracking periods and vice versa be minimized. In order to still more clearly designate the character of the invention the succeeding paragraphs will be devoted to a description of certain practical operating features which possess novelty in the present connection.

One novel feature consists in the use of alternate "idling" periods in the cracking period wherein the heat in refractory fillers following the heating period is utilized to crack oil vapors. As oil vapors pass over a refractory form at the rapid rates characteristic of the present invention, heat is abstracted at such a rate that the surface of the form is cooled below a desired The fixed gases withdrawn at this point may be passed to the same storage as those cracking temperature whilethe interior of the form is still at a considerably high temperature due to the poor heat conductivity of refractory materials. In connection with the present proc- 5 ess therefore, it is proposed that instead of reheating the forms when the surface temperature has fallen below a given point, the flow of the oil vapors be halted until the surface has been returned to its previous high temperature by heat coming from the interior of the form. The flow of the oil vapors is then resumed and the cycle repeated until it is no longer possible to restore the surface temperature to a point above that desired for the cracking.

Fig. 3, A and B indicate diagrammatically the temperature gradients in forms of moderate size at the end of a cracking period in which the form has been used to heat oil vapors and at the end of the combustion or blasting period when the form has been brought up to an optimum temperature for use. It will be seen that the difference in temperature from the surface to the interior of the form is much greater at the end of the cracking period than at the end of the blasting period.

Fig. 3, C, D, E and F show the temperature gradients which will obtain in forms of larger size when idling periods are used to permit flow of heat from the interior to the surface of the forms. It will beobserved that at the end of the idling periods, the curve indicating the temperature gradient has flattened out, that the difference in temperature between the exterior and the interior of the forms decreases after successive cracking periods and that the absolute surface temperature is lower. Conditions such as i the size of the form, the permissible temperature range of cracking, the type of the oil vapors cracked and their rate of flow will determine in general both the absolute and relative time intervals which are best for these alternate cracking and idling periods.

In Fig. 4 the various periods of operation when using four furnaces in parallel and the aforementioned idling periods are indicated. The relative length of the periods is approximated from practice and it will be seen that cracking is taking place in some one of the furnaces at all times. The diagram also indicates that in the case of four furnaces they may be operated in a double parallel sense since two furnaces alternate between themselves in cracking and idling periods, involving merely a shift of the oil vapors from one furnace to thei-other while the other two furnaces are being purged of residual gases and heated by blasting or surface combustion to permit their further use in cracking oil vapors. The use of various types of furnaces and heaters in parallel connection to permit continuous operation along with the various manifolds and valves necessary are generally well known in the art and consequently have not been specifically indicated in the drawings. The use of the idling periods described and the double parallel operation is the feature characteristic of the present invention.

Owing to the evident possibility of varying charging o-il, conditions of operation and type of plant'construction, it is readily understood that numerous instances of operating results might be adduced in support of the commercial value of the present invention. However, the following example will be sufficient to indicate commercial value.

75 h Charging stock used in a series of test runs to determine the best operating conditions was a Mid-Continent product having the following characteristics:

Gravity, A. P. I. 60 F 32.7

The following table shows the results obtained in three runs and indicates that the best conditions considering both the olefin content of the fixed gases and the anti-knock value of the liquid products were those shown in run No. 2. 25

Charging stock Mid-Continent gas oil Run No 1 2 3 Products: by Wt. to charge distillate Gases:

0. 6 1. l 0. 5 1;.4 2.5 .4 8.4 1 un counted osses 34. 0 19. Total oleflus... 34. 4 42.3 Octane number of gasoline,

motor method 104 108 103 Reaction time, sec 0. 016 0.0105 0. 012 Temp. T. of reactor 1400-1290 1600-1420 1320-1220 Pressure, mm. of Hg. absolute. 100 110 110 45 The figures given under "Temperature T. of reactor indicate the range which was obtained during the admission of oil vapors.

As a rule the oieflnic gas mixtures produced by the present process may be utilized directly in various polymerization, condensation and alkylation reactions, with catalysts suitable for accelerating the different types of reactions involved.

The character of the invention and its utility as a branch of the cracking art is evident from the preceding specification and single instance of results obtained by its use, although neither section is to be construed as unduly limiting its generally broad scope.

I claim as my invention:

1. In a process for the pyrolytic conversion of hydrocarbons employing a regenerative type heater wherein said hydrocarbons are passed over the surfaces of previously heated refractory materials and wherein the rate of heat transfer from the hot refractory surfaces to said hydrocarbons is greater than the rate of heat transfer from the interior of said refractory materials to their external surfacesjthe improved method of operation which comprises periodically stopping the flow of hydrocarbons over said refractory'surfaces for a sufficient length of time to permit reheating of the surfaces by the trans- 75 fer of heat thereto from the interior of the refractory material, and subsequently re-establishing the flow of said hydrocarbons to be cracked over the reheated refractory"surfaces 2. A process as claimed in claim 1 characterized in that a plurality of such regenerative type heaters is employed and each heater is subjected to alternate periods of intermittent operation and regeneration and wherein a continuous stream of hydrocarbons to be cracked is alternately passed through and diverted from each heater in such a manner that said stream of hydrocarbons is continuously subjected to conversion in at least one of said heaters.

3. In a process for the pyrolytic conversion of hydrocarbons employing a plurality of alternately operated heaters which are preconditioned by storing heat within refractory materials contained therein and then utilized to heat said hydrocarbons by passing the latter therethrough in contact with the'previously heated refractory materials, the improved method of operation which comprises first passing a stream of the hydrocarbons to be heated through a previously conditioned heater to subject the hydrocarbons to heating for a relatively short time at a rate greater than the rate of heat transfer from the interior of the refractory materials to the surface thereof in contact with the hydrocarbons, then diverting the stream of hydrocarbons to a second previously conditioned heater wherein they are again subjected to such high rates of heating for a relatively short time during which the first heater is allowed to idle and the temperature of the contact surface of the refractories in the first heater is materially increased by heat conducted thereto from the interior of the refractory materials, then diverting the stream of hydrocarbons from the second heater back to the first heater and allowing the second heater to idle, in the manner above described, while the stream of hydrocarbons is again subjected to high rates of heating for a relatively short time in the first heater, thence diverting the stream of hydrocarbons back to the second heater and continuing such alternate operation and idling of the first and second heaters until they require reconditioning to store additional heat in the refractory materials, preconditioning a third and a fourth heater during the periods of alternate operation and idling of the first and second heaters, diverting the stream of hydroheater requires reconditioning, alternately operating and idling the third and fourth heaters, in the manner previously described, while the first and second heaters are being reconditioned and alternately operating, idling and preconditioning each of the heaters in such sequence that the stream of hydrocarbons is continuously subjected to said high rates .of heating.

ROBERT PYZEL.

carbons to the third heater when the second

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