US1715980A - Process of cracking oil - Google Patents

Description

June 4, 1929- ".1. c. BLACK PROCESS OF CRACKING OIL Flled Oct. 20, 1926 .bus-nell 0220119 Kubuntu .n In

INVENTOR. f//aO/ y Patented June 4, 1929.

7 UNITED STATES PATENT oEFlcE.

JOHN C. BLACK, O F DESTREHAN, LOUISIANA.

PROCESS 0F CRACKING OIL.

HEISSUFD Application led October 20, 1926. Serial No. 142,997.

mum temperature the rate of the cracking reaction is augmented with the rise of temperature.- Oils 0f low specific gravity are less easily cracked and require a higher temperature than oils of high specific gravity.

I have found that in cracking an oil the higher the temperature the more rapid the rate of production of carbon whichis formed in the cracking reaction. Thus the amount of carbon which will be formed per unit of time increases with increasing temperature and this increase is not linearly proportional to the temperature but increases more rapidly than the temperature, that is as other than the first power ofthe temperature. Thus, in cracking an oil an increase of temperature from 800 F. to 850 F. causes an increased carbonization over an oilheatedto 800 F., and this increase is considerably less than the increase caused by changing the cracking temperature from 850o F. to 900 F., and the latter is less t-han the increase caused by changing the cracking temperature from 900 F. to 950 F.

This characteristic is more pronounced in the cracking of a heavy oil such as a fuel oil, than in the cracking of a lighter oil such as a gas oil. In a heavy oil the amount of carbon deposition which occurs where the oil is heated to its lowest practical cracking tem perature is consideably more than that oc- `curi-ing when the gas oil is heated to its practical cracking temperature, even though the point at which decomposition sets in in a fuel oil is considerably less than that at which decomposition in the cracking of a gas-oil sets in. Another important consideration resides in the fact that in order to get a formation of 'shbstantial amounts of gasoline from a fuel oil, the temperature to which the fuel oil must be heated is not substantially less than that to which the gas oil must be heated. I have found that unless this be done the fuel oil will decompose to form gas oil with relatively small amounts of gasoline. Therefore, in order to produce gasoline from fuel oil the temperature must be sufficiently high to decompose considerable portions of the gas oil formed by the cracking of the fuel oil.

However, if this be done excessive carbonization will occur.

For example, in operating a well known cracking process in which fuel oil is cracked by passing the oil through a tube under pressure, then in an evaporating chamber under* pressure and in which lighter: bodies are distilled, it is the usual practice to heat the fuel oil in the neighborhood of 900o F. Under these conditions 10% of the charge is precipitated as carbon and the residuum Withdrawn from the evaporator contains as much as 5% of carbon.

I find that a fuel oil maybe cracked economically and etliciently withoutthe formation of material amounts of carbon by avoiding the excessive temperatures usually ernployed in cracking fuel oil to form gasoline. I operate below the cracking temperatures employed in cracking gas oil. That is below approximately 800 F.

I have found that each oil has a characteristie temperature at which it will crack Without the formation of excessive amounts of carbon. If the temperature be raised beyond this point, while there is an increase in the decomposition, there is also an excessive formation of carbon. If the temperature be decreased below this point, while the decrease in the amount of carbon formed is unappreciable, the decomposition falls off very materially. This point is easily determined for each oil by heating the oil under desired pressure to ydifferent temperatures for the length of time chosen to produce desirable decomposition. This point will be called throughout this specification as the temperature of excessive carbonization. I have also found that when operating at the temperature above specified, that carbenes, instead of fixed carbon. are formed. These car benes are soluble in the oil and if sufficient pressure is maintained on the oil to prevent substantial Vaporization during cracking, they will not precipitate.

I have found that by maintaining the oil at this cracking temperature for a prolonged period of time i. e. below its temperature of excessive carbonization I can obtain substantial conversion of the oil. `That is by heating the oil at this lower temperature and over a longer period of time I can get the same amount of oil decomposed without carbonization. I get, however, a different type of conversion than is obtained when operating for a short period at a high temperature, as will appear below.

By regulating'the temperature of the oil so that it 'Will not exceed this temperature of excessive carbonization, and limiting the conversion of fuel oil to form a cracked product of the nature of gasoil, that is, heavier than gasoline, and by supplying the endothermic ally different in character from the originali stock. I have also found that the cracking of the oil in tubes is materially aided and the carbonization materially reduced by the injection of relatively cool oil into the final passes of the cracking coil. I have foundthat by the injection of this oil into the final I obtain a greater yield of decomposed hydrocarbons. Also, I have found thatthe fouling of the tubes is very materially lessened by this injection of oil into the nal passes. I have found that I can operateat a higher temperature without causing excessive decomposition, and thus obtain increased yields. I have also found that the injected hydrocarbons are themselves partially decomposed by the heat contained in the hydrocarbons of the main stream into which they are injected, and also by the heating effect derived from the furnaces while passing through the final passes of the reaction coil. By this injection of oil the heat absorptive characteristics of the oil stream is modified and heat may betransferred to the oil stream without excessive carbonization resulting even if a higher temperatureis employed.

Whilel I do not limit myself to the theory here advanced, I believe that this theory is a very probable explanation of the phenomena observedf .Itis apparent that in operating the system according to my former method, Without the injection of oil into the final passes, that the oil, reaching the final passes, will have been highly cracked with a large formation of lighter oils which do not crack easily. The oil stream also contains heavy bodies, probably formed as a result ofv the cracking reaction. The practical oil man says that the oil becomes dirty. The oil stream and the yfire are manipulated so as to maintain the oil at the chosen cracking temperature. Any transfer of heat that results under the above circumstances goes to carbonize the heavy reduced. The

bodies, depositing a dense carbon on the Walls of the tubes. The heat conductivity is thus tubes .become overheated and passes, l

.excessive carbonization the result is that as more oil advances the carbonization at the film between the oil and tubes becomes more and more severe. This is aggravated by the fact that in systems involving countercurrent passage of oil and combustion gases in the furnace, the oil in the final passes of the coil comes in contact With the hottest gases.

Another result is that this high temperature cracking which results at the surface of the highly heated tubes causes a formation of a large amount of gas which builds up a high vapor pressure. This pressure, if carried to excess, may exceed the operating pressure employed and cause a serious interference in the operation of the process. The introduction of cold, or relatively cold uri-cracked oil into the final passes avoids the difiiculties mentioned above. The injected oil absorbs heat,

in having its sensible heat augmented, from the cracked oil entering the final passes, theref by lowering the temperature of the cracked oil and also checking its cracking. The partially cooled stream then absorbs heat from the combustion gases and the tube wall surface to have its temperature raised to substanthermic character of the cracking reaction.

The tubes are kept from overheating and the as above described is materially reduced.` y

Furthermore, by the injection of this relatively cold oil, any carbonaceous material deposited in the reaction is of softer composition and is more readily removed in the blowing down operation and the heaters can be put back on stream with a smaller loss of time. The injected oil should be so controlled that the temperature of the admixed streams may be such that the decomposition of the injected oi'l'is partially accomplished and to obtain a temperature of the mixture such that the decomposition in the main stream is checked and the carbon of decomposition is minimized. Another' effect caused produce material conversion of the heavy oil.

My invention will be better understood by referring to the accompanying drawing which shows the schematic arrangement ot' one method of carrying out the invention in which:

1 is a tank for holding charging stock. 2 is a pump connecting tank 1 by a line 3 with the analyzer 4 situated in bubble tower 24.

3 is a valve in line 3. 5 is an exit line connecting analyzer 4 with pump 7. 5 is a valve in said line. 6 is a line conecting tank 1 with pump 7. 6 is a valve in said line.I 8 is a line connecting pump 7 with heat exchanger 9. 8 is a valve in said line. 1() is'a crossover line connecting -heat exchanger 9 with heat exchanger 11. 10 is a valve in said line. 54 is a cross-over line connecting heat exchanger 11 with heat exchanger 12. 46 is a line connecting heat exchanger 12 withcoils 14 situated in furnace 17. 13 is a ley-pass line connecting line 10 with coils 14. 13 is a valve in said line. 15 is a cross-over line connecting ,coil 14 with coil 16 situated in furnace 18.

19 is an exit line leading froml the exit of coil 16 through heat exchanger 12. 20 is a crossover line connecting exchanger 11 with exchanger 12. -21 connects exchanger 11 with evaporator 22. 21 is a pressure reducing valve in line 21. 23 is a trap in bubble tower 24. 25 is a vapor line connecting bubble tower 24 with condenser 26. A27 is a look-box sit-uated in run-down line 28. 29 isga collecting tank for condensate issuing from 28. 30 is a gas vent leading from look-box 27. 31 is a line for separating the condensate formed in the bubble tower 24.' 32 is a cooler for said condensate. 33 is a line connecting the cooler 32 with tank 34. 35 is a line connected to the bottom of evaporator 22.l 36 is a pump in said line. 37 is aline connecting the pump 36 with heat exchanger 9. 38-is a line connecting exchanger 9 with cooler 39.. 40 is a line connecting cooler 39 with tank 41. 42 is a line connecting pump 7 with line. 19. 42, 42, 42l are valves in said line. 45 is a line connecting line 42 with one of the final passes of the coil 16. 45 is a valve in said line. 44 is a line connecting line 42 with-the final tube .of coil 16. 51 is a pyrometer at the point o connection of line 45 with tube 16. 47 `is` a water tank. 48 is a line connecting said water tank with line 6. 48 is a valve in said line. 49 is a pressure gauge in line 21 immediately before valve 21. 50 isa pressure gauge in line 42. 52 is a pyrometer at the exit of coil 14. 53 is a pyrometer in line 19. 54 is the aforementioned cross-over line connecting exchanger 11 with exchanger 12. 55 is a gas oil tank. 56 is 'a line connecting said gas oil tank with pump 57. 56 is a valve in said line. 58 is a line connecting tank 34 with pump 57 58 is a valve in said line. 59 is a line connecting pump 57 with'line 42. 59 is a valve in said line. The operation of this process will be understood in connection with above apparatus.

A primary residuum contained in `tank v1,

whichmay be a crude residuum such as a fuel oil, is pumped by pump 7 through line 8 controlled by valve 8', through the heat exchangler 9 and heat exchangers 11 and 12, and via line 46 through coil 14. In coil 14 the oil is heated to the desired cracking temperature, measured by pyrometer52. The oil is then passed into coil 16 where this temperature is maintained and the endothermic heat of the cracking reaction supplied. The temperature may, however, be increased in this furnace. I prefer, however, to operate the invention in such a manner as to maintain the temperature of the oil through the coil 16 constant. Instead of raising the oil to the cracking temperature at the point of exit from coils 14, the oil may reach the cracking temperature at some point in coil 14 and the temperature remain substantially constant through the remaining operation `of coil 14 and through coil 16. The oil is then passed from coil 16 via line 19 through exchangers 12 and 11, where it is cooled down, thus preheating the incoming oil. The temperature to which the oil is cooled should not be below that required to give the desired evaporation in evaporator 22. It too much cooling is effected some of the oilv passing through line 10 is by-passed via line 13 and tubes 14. l The oil issuing from exchanger 11 has its pressure reduced at valve 21 and exits into evaporator 22. The vapors rising from evaporator 22 are reluxed in bubble tower 24. This reflux or fractionation is controlled by regulating the amount of oil passed via pump 2 line 3 through analyzer 4. The oil thus preheated is introduced via line 5 into the main stream entering the intake of pump 7. The lighter lfractions which may be the gasoline produced, are condensed in condenser 26 and the condensate passing through lookbox 27 collecting via line 28 in tank 29. The gases issuing from look-box 27 are collected via line 30. A portion of the oil issuing from the exit of pump 7 may be passed via lme 42 controlled by valves 42', 42 and 42 into either the final passes of coil 16 or into the final tube of said coil, or into line 19. Instead o using, or in addition to using the primary residuum. from tank 1, a gas oil from tank 55 maybe pumped via pump 57 into line 42 by the requisite control of valves 42', 42, 42', valve 56 and valve 59. Instead of using gas oil, or in addition tousing the gas oil, a cracking product in tank 34 may be pumped via line 58 by the requisite control of the valve 58' and the other valves mentioned, via pump 57 vila line 59 into line 42.

The amount of injected oil vis controlled `to check the cracking in the final passes andatov n crack a portion of the injected oil.`

meet the specifications for bunker fuel oil C given in Technical Paper 323A of the Bureau of Mines, contained in tank 1 is pumped'under pressure sufficient to prevent any substantial Vaporization in the coils, and is heated in coils 14 to about 800 F. This temperature is maintained in coil 16 to subject the oil to heat at this temperature for a period of about twenty to twenty-five mnutes, or more, i. e. for a period suiicient to cause the desired decomposition. The temperature of the oil is modified by the injection of oil in any of the manners described above, for instance, cold oil may be injected via 45 to drop this temperature from 50o F.v to 100 F. The oil is then heated up and it passes through the rest of the coil so that its temperature when measured at point 53 shall be 800o F. or lower for example between 750- 800.` Or the oil may be injected directly via 44 or via valve 42 to drop the temperature of the oil from 800o F. to about 750 F. The oil is then passed through the exchanger 12 and 11, and this temperature reduced to about 550- F. The oil in passing through the coil is maintained under a pressure sulicicnt to prevent substantial vaporization. In using fuel oil this pressure may be in the neighborhood of 500 pounds measured in the terminal gauge 49. l The pressure is reduced to substantially atmospheric and the oil is vaporized in evaporator' 22. The vapors rising in bubble tower 24 are refluxed and the redux controlled by the passage of oil through analyzer 4. Vapors issuing from 25 are gasoline and condensed in 26 and collected in 29. An intermediate fraction is drawn ofi' from 31, cooled in 32 and collected in tank 34. This condensate-is an artilicial gas oil made by the cracking of the fuel oil. is the residuum removed from evaporator 22 vla pump 36 is cooled down in heat exchanger 9 and cooler 39, and collected in 41, and will be found to be a fuel oil which will also meet the Government specifications for bunker fuel oil C specified above. In other words, .the cracked product formed during the cracking reaction is removed by this evaporation and refluxing. By limiting the temperature below the point of active carbonization the concentration of the carbon will be such as to be less than 0.25% required by this Government specification. In operating in the above manner it will be found that about 5% of gasoline 1s formed and about 25% of a gas oil will be separated via line 31.

The oil injected via line 42 may be, as was stated previously, I a primary residuum in tank one,l or may be a portion of a product collected 1n tank 34, or may be of the nature of a gas oil in tank 55. By the injection of this oil I have found that the excessive carbonization which some times occurs in the final passes of the tube ismaterially reduced,

permitting of the using of slightly higher The fuel oill which temperatures than would be possible if this injection were not used. But even by the use of this injection oil the temperature must be limited below the point of active carbonization or excessive carbonization in coil 16 will occur. The injected oil may be cracked by the heat in the main stream of oil. This cracking is aided by the sudden rise in temperature through which the oil is carried at the moment of injection. This effect of the sudden rise in temperature I have termed the shock effect.

The above is not to be taken as limiting my invention, but merely as illustrative of the best manner of carrying out my invention, which I claim to be:

1. A process of cracking crude oil residuum for the production of a relatively small amount of low vboiling hydrocarbons, a relatively larger amount of higher boiling hydrocarbons, and a residuum suitable for fuel oil, which comprises, passing a crude oil residuum through a series of cracking coils, under super-atmospheric pressure and at a temperature sufficient to lightly crack the same, and preventing further destructive decomposition of the hydrocarbons of said crude oil residuum by the introduction of a cooler hydrocarbon 'oil into the final passes of the last cracking coil, in quantities sufficient to maintain'the said crude oil residuum below the temperature of excessive cracking and carbonization.

2. A process of cracking crude oil residuumfoar the production of a relatively' smalt amount of low boiling hydrocarbons, a relatively larger amount of higher boiling hydrocarbons, and a residuum suitable for fuel oil, comprising, passing a crude oil residuum through a series of cracking coils, under super-atmospheric pressure and at a tempera- ,ture suiicient to lightly crack A'the same, thereby preventing the destructive decomposition of the hydrocarbonsv to carbonaceous material to any substantial degree; and introducing a cool hydrocarbon oil into the final passes of the last cracking coil, 1n quantities sullicient to prevent further cracking of therst mentioned oil substantially as described.

3. A process of cracking crude oil residuum for the production of a relatively small amount of low boiling hydrocarbons, a relatively larger amount of higher boiling hydrocarbons, and a residuum Suitable for fuel oil, comprising, passing a crude oil residuum through a series of cracking coils, under super-atmospheric pressure and at a temperature suficient to lightly crack the same, andsubstantially preventing the destructive decomposition to carbonaceous material of any of'said crude oil residuum by the intro- -duction of a cooler hydrocarbon oil into the final pass of thelast coil, in quantities sufcient 'to maintain the said crude oil residuum below the temperature of excessive cracking and carbonization.

4. A process of cracking fuel crude oil for the production of a relatively small amount of gasoline stock, a relatively larger amount of higher boiling oil and a residuum suitable for fuel oil purposes, comprising, passing said crude oil through a series' of cracking coils under super-atmospheric pressure at a temperature just suiicient to lightly crack the same, and heating for a prolonged period of time while passing through the cracking coils, and substantially preventing the destructive decomposition to carbonaceous material of said crude oil by the int-roduction of a cool oil into the linal passes of thelast cracking coil, in quantities sufiicient to maintain the crude oil below the temperature of excessive decomposition, and to lightly crack the said introduced cool oil.

5. A continuous process of cracking fuel oil at relatively low cracking temperatures for the production of a minor portion of low boiling hydrocarbons, a larger portion of relatively higher boiling hydrocarbons, and a residuum suitable for fuel oil, comprising, passing fuel oil through a series of cracking coils under super-atmospheric pressure over a prolonged period of time while passing through the cracking coils, and maintaining a relatively low cracking temperature to crack the same lightly, and substantially preventing the destructive decomposition of carbonaceous material of said fuel oil by the introduction of a cooler oil into the final passes of the last cracking coil, in quantities sufficient to immediately cool the rst mentioned oil below the cracking temperature, substantially as described.

6. A continuous process of cracking fuel oil at relatively low cracking temperatures for the production of a minor portion of low boiling hydrocarbons, a larger portion of relatively higher boiling hydrocarbons, and a residuum suitable for fuel oil, which comprises, passing fuel oil through a series of cracking coils under super-atmospheric pressure, at relatively low cracking temperatures to crack the same lightly,.and preventing the destructive decomposition to carbonaceous material of substantially any of said fuel oil by the introduction of a cooler fuel oil into the last passes of the final cracking coil, in quantities suiicient to cool the irst mentioned oil below the temperature of excessive cracking, vaporizing the lower boiling hydrocarbons together with the relatively higher boiling hydrocarbons produced, fractionally separating' the lower boiling hydro carbons from the higher boiling hydrocarbons, and separately withdrawing an unvaporized residuum suitable for fuel 011.

JOHN C. BLACK.

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