US2126400A - Process of and apparatus for producing lower boiling products from mineral oils - Google Patents

Description

Aug. 9, 1938. w LEAMON 2,126,400

PROCESS OF AND APPARATUS FOR PRODUCING LOWER BOILING PRODUCTS FROM MINERAL OILS Filed Dec. 8, 1930 gwumto'o I coil and is thus subjected to extremely rapid Patented Aug. 9, 1938 UNlTED STATES 2,126,400 raoorss or AND APPARATUS roa PRO- DUCING LOWER BOILING PRODUCTS FROM- MINERAL OILS William G. Leamon, New York, N. Y., assignor, by

mesne' assignments, to Houdry Process Corporation, Wilmington, DeL, a corporation oi'Delaware Application December 8, 1930, Serial No. 500,886

10 Claims.

This invention relates generally to processes of and apparatus for producing lower-boiling products from mineral oils; and it relates more particularly to the treatment of relatively heavy mineral oils of the petroleum type for the manufacture of lower-boiling products I therefrom, such as motor fuel and the like.

In Patent No. 1,769,789, dated July 1, 1930, this applicant has'described a process of converting heavy mineral oils into low-boiling products of the motor fuel type in which the mineral oil to be converted or cracked is first heated to a temperature below that normally efiective for cracking, but sufiiciently high to vaporize a substantial portion of the oil while leaving a higherboiling portion, including tarry constituents, une vaporized and commingled with the vapors. This mixture of oil vapors and unvaporized relatively heavy liquid oil is conducted to a separator which removes the unvaporized oil from the mixture, the separated vapors then being conducted through suitable superheating elements or coils where they are brought to a temperature that is amply high to efiect cracking, but so rapidly as to avoid such extensive cracking at this stage as would cause excessive deposition of carbon, whereupon the vapors thus rapidly superheated are directed into a cracking chamber maintained at a temperature somewhat lower but still effective for cracking, the .vapors traveling through this cracking chamber slowly enough to give ample time for efiective vapor-phase cracking to take place. The resultant cracked vapors are then appropriately treated to recover therefrom a lower-boiling,condensate, such as a motor fuel condensate.

This procedure is very effective and has been very successful in commercial operation. The

high temperature or superheating coils, when operated in accordance with the teaching of the aforesaid patent, remain almbst entirely clean for long periods of time.

It has been found, however, that a certain very minute'amount of liquid-phase material of such small size and mass that neither mechanical separating means nor scrubbing can remove it, is carried over into the superheating coils with the vapors and that when this extremely finely divided liquid-phase material, which is usually referred to as smoke, enters the superheating heating, a certain amount of it decomposes and tends to deposit carbon in the superheater coils. This carbon deposit is gradually built up until it eventually causes shut-down of the plant due to accumulation of carbon in the superheating coils.

A principal object of this invention is to improve the process generally set forth above in such a way as to eliminate the stated objections and to provide a procedure whereby the entrained liquid-phase material in the vapors is practically all converted into vapor phase without serious deposition of carbon before these vapors are subjected to extremely rapid heating in the superheater coil.

Another object of the invention is to provide a procedure whereby such conversion of the entrained liquid-phase material into vapor phase can be carried on continuously and simultaneously with the carrying out of the general process and in an .eflicient and economical manner.

Another object of the invention is to provide apparatus of an improved type whereinthe process as modified in accordance with the present invention may be carried out to advantage.

Other and more specific objects and advantages of the invention will appear more fully hereinafter.

In its most advantageous practical embodiment, the present invention is. characterized by the fact that the previously separated substantially saturated vapors or vapors carrying entrained finely-divided liquid-phase material are superheated relatively slowly to a moderately higher temperature and then rapidly superheated to a much higher temperature effective for cracking.

A further explanation of' the invention can best be given in connection with a concrete illustrative embodiment thereof which will now be described in connection with the accompanying drawing in which Fig. l is a more or less diagrammatic or schematic representation, partly in section, of one form of apparatus that can be used to advantage in practicing the process of the invention, and Fig. 2 is a sectional view of the heater, taken on the line 2 --2 of Fig. 1, showing a top plan of the intermediate heating coil.

Referring to the drawing, l represents a supply pipe controlled by liquid-level regulating valve la, through which heavy oil to be cracked enters the feed tank 2 where it mixes with hot condensate, to be referred to hereinafter. A topped crude petroleum is an example of a heavy mineral oil that can be successfully cracked or converted by the present process, but it is to be understood that other kinds of mineral oil and residua may be used as starting material. The

temperature of the composite oil in tank I may vary from 350-550 I". and in a typical instance averaging around 500 F. From tank 2 the composite oil passes through pipe line 3 and is pumped under pressure by pump 4 to the vaporizing coil or relatively low temperature heating element I of the heater 6 which may desirably be a pipe still. The pressure at the pump discharge may vary from -100 pounds per square inch and in a typical instance may be in the neighborhood of 90-95 pounds per square inch. A heat exchanger diagrammatically shown at I is preferably provided in pipe line 3 between the pump and they it reaches the heater the temperature of the oil at the inlet to coil 5 is between 500 to 700 F., averaging around 600625 F. in a typical instance. The composite oil is heated in the va porizing coil 5 to a temperature most desirably ranging from about 700 to 850 F., the exact temperature most desirable to employ being dependent somewhat upon the particular oil employed as starting material. A temperature within this range, while insufllciently high to eifect extensive cracking in the relatively short time otheating, is nevertheless high enough to vaporize practically all that lighter portion of the oil which it is desired to permit toenter the cracking or converting zone. The mixture of vapors and liquid particles of unvaporized oil associated therewith leaves the initial heating or vaporizing coil 5 and enters suitable mechanical separator means 9, in the present instance shown as an upright separator of the vertical cylindrical type. The pressure in the separating means is not much lower than that under which the mixture of liquid and vapors leaves coil 5, ranging from about 30 to 90 pounds per square inch, averaging around 70-75 pounds per square inch in a typical instance; and while there is some drop in temperature, of the order of 5 to 15 1''. for example, varying with the particular installation, the temperature of operation, and the rate of through-put, there is no extensive reduction of temperature in the separator. The

temperature in the separator may vary between TOW-850 F., averaging around 800 F. in a typical amount of entrained oil in liquid-phase partly due to incomplete separation and partly due to incipient vapor condensation, and this liquidphase oil is in such a finely divided state, some of the particles possibly being of molecular or near-molecular size, that it cannot be removed by the separator. A part of this entrained liquidphase oil will carbonize when subjected to the very rapid heating to high temperature in the superheater coils and eventually cause a shut-down due to the slow accumulation of the carbon on the inventionisto provide an-efiective and econom- I ical procedure for preventing this entrained liquid-phase material or "smoke" from entering the high temperature or superheater coils and causing them to carbonize. This is done in the present instance by converting, 'or reconverting, the finely divided entrained liquid-phase material into vapor phase by heating the wet or substantially saturated vapors from the separator at a relatively moderate rate before passing them to the high heating rate superheating'coils.

This procedure may be carried out in various ways within the broad scope of the'invention, but in the example illustrated the wet vapors from the separator 9 pass through exit pipe H to a heating element or coil I! which may be termed an intermediate or moderate heating or moderate rate superheating zone. Here the wet or substantially saturated vapors are superheated relatively slowly to a moderately higher temperature with the result that-substantially all of the entrained liquid phase material is converted into the desired vapor phase without serious deposition of carbon. This coil may vary in size and arrangement within the broad scope of the invention, but in a typical instance the intermediate heating coil i2 may comprise a number of lengths of tubing connected in parallel and so disposed in the heater that the rate of heat transfer is of the order 01' three to eight thousand or less B. t. u.s per square foot per hour. As a matter of fact, however, the

.lower limits to the rate of heat transfer are governed mainly by practical considerations as to the size of the intermediate heating coil that may be reasonably employed in a given apparatus. Obviously, the lower the rate of heat transfer, the greater the amount of heating surface required. This coil should, for example,.have a'surface of sufllcient size to raise the temperature of the vapors passing through it by an amount of say 15to 50". F4: approximately 25 F. being considered an average required in ordinary operation. In general, the actual temperature rise needed in coil i2 is simply that which will suflice to convert substantially all of the liquidphase material entering it into vapor phase and the actual amount of heat input varies with the nature of the oil being processed .and the temperature at which the separator is being operated.

In this .intermediate heating coil i2, usually referred to as the vapor drier", the tubes are preferably arranged in'parallel so as to provide a slow velocity of vapors through this intermediate heating zone where the mean temperature diiference between the temperature of the tubes and the temperature of the vapors is small with consequent slow rate of heat transfeni A further advantage oi the parallel arrangement of tubes is the very low pressure drop that results with the very largecross-sectional area available for'the vapor flow. With this large cross-sectional area any small amount of carbon which might be precipitated from the entrained liquid phase oilbeiore or during its conversion to vapor phase presents such a relatively .small impedithe effect when the wet vapors are introduced.

directly into the superheater coils which are of relatively small cross-sectionalarea and in which a very small deposition of carbon may offer such a high resistance to vapor flow as to cause the plant to be shut down and the deposit removed even. though the actual quantity of carbon deposited is very small. a

The arrangement of this" intermediate coil or vapor drier" l2 in the heater may also vary considerably within the broad scope of the invention, but in general it should be arranged so that it is protected from the very high temperatures of the fire box. In the example illustrated, it is arranged adjacent the roof of the furnace and is heated by conducted heat from the fire box, being shielded or protected by a partition or layer It of fire brick or similar refractory material. This coil may, however, be heated by the hot combustion gases by convection or, by radiant heat andif heated by radiant heat, the superheating or high temperature coils may be used as a shield to protect it from the high temperatures of the fire box, but, as a matter of fact, any arrangement that reduces the rate of heat input into the coil to the proper value may be employed.

From the intermediate heating coil l2 the dry vapors pass by pipe M to the superheater or high temperature heating coil or element l5, which is subjected to more intense heat than coil i2, being directly exposed to the radiant heat from the fire box. In the superheater coil the rate of heat transfer is usually of the order of 10 to 20 thousand B. t. u.s per square foot per super-heating to a moderately elevated temperature before subjecting them to the actual cracking, or converting temperatures. It is also obvious that this method of preparing dry vapors for processing purposes may be employed wherever highly superheated vapors are required as in the so called hydrogenation process for producing motor fuels etc.

The resultant cracked vapors from cracking unit I! pass through pipe 8 to the heat exchanger I and then by pipe I! to the fractionating column 20. Here relatively high boiling constituents are separated and collect in tank 2 to be recycled. The vapors leaving the top of the column pass by pipe 2| to a condenser 22 and a crude motor fuel condensate collects in receiver 23 from which it may be withdrawn through valved outlet 24, fixed gases passing off through pipe 25. A pump 26 is arranged to withv I draw crude condensate from receiver 23 and return the same through pipe line 21 to the top of fractionating column 20 in order to aid effective functioning of the latter.

The effect of this invention on the rate and quantityof carbon deposition which may take place in a cracking plant is illustrated by the following table which sets forth the actual results of operating the same unit both with and without the vapor drier".

Coke in vapor heating coils Pounds of vapor per lb. oi coke Coke percent by weight of oil prooesse Rate of heat transfer in cokcd tubes.-.

Rate of heat transfer in vapor dryer Relative rates oi heat transfer hour, 14 to 15 thousand being usual in a typical instance. The dry vapors 'pass at high velocity through coll t5 and are very rapidly brought to a temperature" varying between 10001100 F.,

averaging around .1050 F. in a typical instance, but do not remain therein long enough to permit substantial cracking or carbonization to occur there. From superheater coil IS the superheated vapors pass through pipe IE to the vapor-phase cracking or reaction unit H, where the vapors are maintained at a sufficiently high temperature and for a sufficiently long time to enable effective cracking or conversion to take place. The cracking zone I1 is preferably well lagged with suitable heat insulation, as shown at l8, so that, by operating with a small pressure drop between the outlet of superheater coil 15 and the cracking zone ll, said cracking zone may be maintained at effective cracking temperatures entirely by the superheat of the oil vapors entering the same and without the employment of external heating. The cracking chamber l1 most desirably contains a mass of porous adsorptive contact material I!' inert to sulfur, nitrogen and carbon under the conditions of operation, through which the vapors are obliged to pass. Pumice is an example of such material. However the invention is not restricted to the use of such material; or any contact material.

In the practice of.this invention in some instances it may be desirable to build superheater coll l5 of such size and operate it in such a manner that the actual cracking of the oil vapors will take place in the coil and not in a separate reaction or crackingchamber. Obvi- It is to be understood that the foregoing speciflc examples of process and apparatus and the specific figures are given merely for the purpose of explaining the principles of the invention by means of concrete operative embodiments thereof that have given satisfactory results in practice, and that the invention is in no sense limited to the particular details of process and apparatus hereinabove given.

What is claimed is:

l. The process of converting mineral oil into lower-boiling products, which comprises subjecting mineral oil traveling in a stream of relative small thickness to heat at temperatures below cracking temperatures but suflici'ently high to vaporize a desired portion of said oil while leaving heavyconstituents of the oil as liquid commingled with-the vapors, separating such liquid from the vapors, passing said vapors relatively slowly through a relatively moderately-heated coil until they attain a temperature in the neighborhood of 875 F. but below vapor phase cracking temperature, then passing said vapors at high velocity through a relatively highly-heated coil until they attain a temperature not exceeding about 1100" F., discharging the vapors into a "cracking chamber wherein the average temperature is below 1100 F., but high enough for effective cracking, allowing said vapors to travel through said chamber slowly enough to permit extensive cracking to occur, and recovering a relatively low-boiling condensate from the cracked vapors.

2. Apparatus for converting mineral oil into lower-boiling products which comprises, in combin'ation, means for heating oil to obtain' oil vapors'mixed with liquid-oil, mechanical separating means connected to such heating means and into which such vapor-liquid mixture is disoil in the vapor phase, which consists in passing a moving stream of such oil through a primary heating zone and therein heating the oil to a temperature at which portions thereof will vaporize without molecular decomposition, substantially separating such vapors in an externally unheated zone from the remaining portions of the oil which do not vaporize without molecular decomposition, passing said vapors in a confined moving stream through an intermediate. heating zone possessing a higher temperature than said primary zone to effect vaporization of the entrained unvaporized oil present in said vapors as .a mist or suspensoid-to reduce said vapors to a substantially dry moisture-free state without permitting any appreciable cracking thereof to take place, then passing said dry vapors in a confined moving stream at a velocity materially greater than the velocity of the vapors in the intermediate-zone through an elongated cracking zone of restricted cross-sectional area wherein said vapors attain a cracking. temperature in excess of 1000 F., and utilizing the same products of combustion which are employed to heat the cracking zone to a high temperature for heating the intermediate drying zone'to a lower temperature.

4. The method of cracking hydrocarbon oil into vapor phase, which consists in passing a moving stream of such oil through a primary heating zone and therein heating the oil to a temperature at which portions thereof will vaporize without molecular decomposition, substantially separating such vapors in an externally un-. heated separating zone from the remaining portions of the oil which do not vaporize without molecular decomposition, passing said vapors in a confined moving stream through an intermediate heating zone possessing a higher temperaturethan said primary zone to eifect the vaporization of entrained unvaporized oil present in said vapors without any appreciable cracking of the vapors taking place, then directly passing said dry vapor from the intermediate heating zone and without reduction in its total weight through an elongated conversion zone of restricted cross-sectional area, wherein said vapors attain a conversion temperature in excess of 1000 F., and causing the vapors totravel at a materially greater velocity through said conversion zone than the velocity of travel thereof through the intermediate drying zone by varying the cross-sectional area of the said intermediatedrying zone and the conversion zone.

5. Apparatus for converting mineral oil into lower boiling products which comprises in combination a bank of tubes adapted to heat oil and generate vapors therefrom, a separating chamber in which the oil heated in said tube bank is separated from the vapors generated therein, a sec ond tube bank towhich said vapors are conducted and in which said vapors are mildly heated, a super-heating tube bank receiving vapors from said second tube bank and in which said vapors are rapidly heated to a temperature above their cracking temperature, said second tube bank comprising-a series of tubes connected in parallel whereby the vapors are caused to pass therethrough at a speed relatively slower than their speed through said super-heating bank, and a cracking chamber adapted to receive vapors from said super-heating tube bank.

6. The process of producing lower-boiling products from mineral oil which comprises heating mineral oil to vaporize a substantial portion thereof below effective cracking temperature while leaving a high-boiling portion including contained tarry matter substantially in unvaporized condition but commingled with the vapors, separating the oil into the unvaporized high-boiling portion and wet vapors and removing the former, further heating said wet vapors com paratively slowly through a relatively small temperature range sufficient to vaporize entrained liquid but not sumcient to raise the temperature to an eflective vapor phase cracking temperature, then superheating said dried vapors comparatively rapidly through a relatively great temperature range to an effective cracking temperature, maintaining the vapors at cracking temperature for a period of time long enough to effect extensive cracking, and recovering a desired lowerboiling product from the cracked vapors.

7. The process of producing lower-boiling products from mineral oil which comprises heating mineral oil to produce substantially saturated vapors therefrom, further heating said saturated vapors comparatively slowly through a relatively small temperature range sufficient to vaporize entrained liquid but not sufficient to raise the temperature to an eflective vapor phase cracking temperature, then superheating said vapors comparatively rapidly through a relatively great temperature range to an effective cracking temperarelatively heavy mineral oil and vaporizing a.

substantial portion thereof below effective cracking temperature while leaving a high-boiling portion including contained tarry matter substantially in unvaporized condition but commingled with the vapors; separating out the unvaporized high-boiling portion, heating said vapors comparatively slowly through a relatively small temperature range sufficient to vaporize entrained liquid but insufficient to raise the temperature to an effective vapor phase cracking temperature, then superheating the thus dried vapors through a relatively great temperature range to a temperature in excess of that required for effective cracking but so comparatively rapidly that the vapors leave this stage of the process largely uncracked, then maintaining said vapors in a cracking zone kept at effective cracking temperature by the superheat of said vapors for a period of time long enough to effect extensive cracking, and recovering a relatively low-boiling condensate from the cracked vapors.

9. The process of producing lower-boiling products from mineral oil which comprises heating mineral oil to produce substantially saturated vapors therefrom, further heating said vapors comparatively slowly through a relatively small temperature range suflicient to vaporizeentrained liquid but not sufficient to raise the temperature to an effective vapor phase cracking temperature, then superheating said vapors comparatively rapidly through a relatively great temperaformer, further heating said wet vapors comparatively slowly through a relatively small temperature range sufficient to vaporize entrained liquid but not sufiicient to raise the temperature to an effective vapor phase cracking temperature, then superheating said dried vapors comparatively rapidly through a relatively great temperature range to an efiective cracking temperature and subjecting the highly superheated vapors to converting conditions for the production of lower 10 boiling products.

WILLIAM G. LEAMON.

Images