US1927829A - Process for treating hydrocarbon oils - Google Patents

Description

Sept. 26, 1933. A. E. HARNSBERGER ET AL PROCESS FOR TREATING- HYDROCARBON OILS Filed Jan. 25, 1930 C L. Smith WK 0. MW

dtto'nmq Patented Sept. 26, 1933 PROCESS FOR TREOATISNG HYDROCARBON Audley E. Harnesberger Chicago, Ill., assignors and Clyde L.. Smith, to Gyro Process Company, Detroit, Mich., a corporation of Michigan Application January 25, 1930. Serial No. 423,519 1 Claim. (01. 196-61) This invention relates to improvements in the art of effecting through heat treatment molecular decomposition of heavy hydrocarbon oils to pro duce therefrom lighter hydrocarbon oils which are suitable for use as motor fuels. The invention has particular reference to high temperature oil cracking systems wherein the oils undergoing decomposition or cracking reactions are maintained in the vapor phase at reaction producing temperatures usually in excess of 1000 F.

It is an outstanding object of the present in-' vention to treat the oils charged to the system to preliminary heating for the purpose of effecting an initial vaporization of the charging stock prior to the circulation of the latter through furnace tubes, in order to permit of the removal from said charging stock of the high boiling point tarry fractions which, if subjected to heat in a tube still, produce large carbonaceous deposits on the inner walls of such tubes and seriously interfere with the proper heating of the desired oils passing through such tubes.

It is a further object of the invention to effect such preliminary heating of the charging stock by bringing the latter into direct contact with the highly heated cracked vapors issuing directly from the outlet of the high temperature conver sion zone of the system, in order that the self contained heat present'in the cracked vapors may be economically and advantageously employed in vaporizing the charging stock, to reduce the temperature of the cracked vapors sufficiently to permit of the desired fractionation of the cracked oils, and at the same time to provide the system with a recycle or charging stock of a clean character and of desired gravity which, when circulated through the furnace heated tubes of the system, will be substantially entirely free of those objectionable heavy oils which tend to form carbon deposits on the inner walls of the tubes.

Earlier systems of vapor phase conversion require carefully selected charging stocks which are, in the main, devoid of carbon producing fractions. By the present invention, however, any

4 type of charging stock may be successfully utilized, since the system functions to automatically reject those fractions which may interfere with the proper operation of the system and yet effects a high rate of conversion of the desirable or usable fractions of the charging stock.

For a further understanding of the invention reference is to be had to the following description and to the accompanying drawing, wherein the single figure illustrates a flow diagram giv- 65 ing the arrangement of the apparatus used in connection with the invention and the flow of oil through and from such apparatus. I

Referring more particularly to the drawing,

the numeral 1 designates the setting of a furnace.

The interior of the furnace is provided with a transversely extending bridge wall 2, which divides the furnace internally into combustion and tube chambers 3 and 4 respectively. The combustion chamber is provided with burners 5 for developing heated furnace gases, the latter passing generally upwardly through the combustion chamber, then sweep horizontally along the roof of the furnace and turn substantially downwardly for movement through the tube chamber 4. The lower portion of the tube chamber is provided with a horizontally directed stack outlet or duct 6 which communicates with a vertically disposed stack '7 of any desired height to effect the necessary'draught or circulation of fumace gases through the setting.

Arranged in the duct 6 is a bank 8 of oil preheating or vaporizing tubes. This bank of tubes is preferably heated by the waste gases discharged from the tube chamber 4 and permits of the efficient utilization of the heat developed by the furnace 'so that the gases discharged from the stack '7 will be of minimum temperature. The charging stock enters the bank of tubes 8 by way of the pipe line 9 and is forced serially through the tubes of said bank in order that the oil may be heated to a vaporizing temperature of approximately 700 to 825 F. Ordinarily, little or no cracking of the oil takes place in the tube bank 8.

The oil discharged from the bank 8 passes by way of the pipe line 10 to an evaporator 11 wherein the high boiling point oils, which remain in a liquid state at the temperatures specified, are dropped to the bottom of the evaporator and withdrawn by way of the valved outlet 12. These high boiling oils may be disposed of as fuel oils. The lighter oils which are in a vaporlzedcondition in the evaporator 11, pass. overhead from the latter by way of the outlet line 13 and are delivered to a series of drying tubes 14 arranged in the low temperature side of the tube chamber 4. superheated steam may be introduced into the outlet line 13 by way of the, steam line 15 in desired quantities. However, the introduction of steam at this point is optional, since the system will function adequately in many instances without the employment of steam.

The drying tubes 14 are of relatively large cross-sectional area, for example, eight inchesin diameter, and the oil vapors flow serially through will have little or no practical effect. on the transmission of heat to the vapors or in the matter of seriously obstructing oil vapor flow through the tubes.

After the vapors have been dried by passage through the tubes 14 they are continuously transmitted to a bank of cracking or converting tubes 16 which are arranged in the radiant heat section of the furnace 1, preferably around the sides and top wall of the combination chamber 3. In the operation of systems of this kind it is desirable to raise the temperature of the oil vapors which enter the conversion zone rapidly from a non-conversion or drying temperature to an active cracking temperature in excess of 1000 F. A very practical method of accomplishing this consists in placing the first bank oftubes comprising the cracking section in the radiant heat zone of the furnace, asindicated at 16. It will be understood that the rate of heat transfer by radiation is proportional to the fourth power of the difference between the absolute temperature of the radiating and absorbing bodies, whereas the rate of heat transfer by convection is proportional to the first power of the difference between the absolute temperature of the hot gases and the heat absorbing structure. Accordingly, where heat transfer is effected simultaneously by. radiation and convection, the temperature of the heat absorbing'structure may become excessive. Therefore, to prevent injury to the tubes 15 it is important that these tubes be kept clear of carbon deposit and that the velocities of oil travel through said tubes be maintained at a relatively high point in order that the heat applied to said tubes may be quickly absorbed by the rapidly moving oil vapors and carried away. The drying tubes serve to eliminate carbon. deposit in the cracking tubes 16, and since the latterare of relatively small cross-sectional area the velocity of oil vapor travel therethrough is high, usually in excess of 2500 feet per minute. The employment of substantially one per cent of steam by weight in the oil delivered to the cracking tubes is thought to minimize carbon deposit and maintain vapor velocity.

After the oil has been discharged from the bank of tubes 16 it possesses a temperature in excess of 1000 F. and less than 1200 F. Since" cracking is a product both of time and temperature, it is necessary to maintain the vapors for a desired period of time at a particular cracking temperature to secure a desired rate of conversion. Careful regulation in this respect is required to secure a maximum yield of a desired end product. If the desired end product is a motor fuel distillate, care must be taken to avoid overheating the oil vapor when at a cracking temperature to prevent the formation of excessive quantities of fixed gas, which possess a lower economical value than the motor fuel distillates. On the other hand,care must be taken to avoid underheating the vapors, in order to secure a maximum yield with each throughput of the cracking stock of the desired end point distillate and to provide for eflicient operation. Also, the tubes should be relatively placed to secure a uniform heating action to overcome unequal heating of the -oil vapors passing therethrough.

. is done to accommodate for the expansion of the walls of the tubes.

In the attainment of these ends the chamber 4 is provided with a horizontally placed row of tubes 1'7, which are located in the upper portion of the chamber 4 and are subjected to a high degree of furnace heat which is of such a char- 30 acter that the oil vapors discharged from the tubes. 16 are constantly heated while passing through the tube row 1'7. This rate of heat input is such as to overcome loss of heat due to the endothermic reactions taking place in the oil vapors while undergoing cracking. From the tubes 1'? the oil vapors flow serially through a row of tubes 18 arranged in the chamber 4 immediately above the drying tubes 14, and from the tubes 18 the oil vapors are passed serially through a third row of tubes 19, which are disposed between the tube rows 17 and 18. If desired, the tubes 1'7, 18 and 19 may be of progressively increasing cross-sectional area. This vapors due to the temperature rise and also to the drop in pressure due to decreased frictional resistance between the moving oil vapors and The largest part of this increase in volume is undoubtedly due to the drop in pressure rather than the increasein temperature. Thus the oil vapors pass ng through the tubes 16, 17, 18 and 19 are constantly heated to secure a continuation of the desired cracking reactions, and since heat is being applied or delivered to the oil vapors flowing through the tubes 17, 18 and 19 it follows that these tribes are, not to be considered as mere soaking drums or sections but as active cracking tubes.

From the tubes 19 the cracked oil vapors flow through a pipe 20 and enter a conversion or cracking arrester 21. This arrester consists of a closed vessel into the lower part of which the pipe 20 extends. Due to the fact that the vapors discharged from the converter possess a high temperature, usually in excess of 1000 F., the economy of the system from the standpoint of heat consumption can be improved by utilizing advantageously the self-contained heat present in these cracked vapors. To secure this end a charging stock, such as fresh topped crude is advanced through a pipe line 21' by means of a pump 22. From the pump 22 the charging stock is advanced by a pipeline 23 provided with a valve 24 into the pipe line 20 wherein the charging stock is actively intermingled with the hot cracked vapors so that heat exchange takes place whereby the charging stock is vaporized, particularly the lower boiling fractions thereof and, in all probability, some cracking takes placeby this operation. However, the products discharged from the pipe line 20 into the bottom of the arrester are preferably fractionated in order that the heavy liquid oils which are not in a vaporized state will settle to the bottom of the arrester, where they may be withdrawn by way of the valved outlet line 25. It has been found that by eliminating this fraction of oil from the systhrough a heat exchanger 39 which surrounds the, I

- tageously the lower boiling oils.

tact with the heated provided with a second vided with fractionating battles 26 which insure the removal of the high boiling fractions from Above the baille 26 there is provided a liquid trap 2'7 from which extends a valved pipe line 28 which leads to the lower portion of a fractionating tower 29. The top of the arrester is provided with an overhead line 30 which also leads to thetower 29 and enters the latter at a point immediately above the line 28. The vapors thus delivered to the tower 29 are fractionated so that the vapors discharged overhead from the top of the tower 29 and which pass to storage will possess a boiling range approximating that of gasoline. 1

It is necessary in order to minimize carbon deposit to sharply reduce the temperature of the oil vapors entering the arrester from a cracking temperature to a nonracking temperature. This is best accomplished by means of the spray coil 31 which is located in the top of the arrester. This coil is supplied with fresh oil from a working tank 32. From the outlet line 33 of this tank a pump 34 operates to positively force the.

oil-through a line 35 which is suitably valved and is connected with the coil 31. In this manner fresh quantities of cold oil are discharged in the top of the arrester coming into intimate conascending vapors for the purpose of effecting a substantially instantaneous drop in the temperature of such vapors from a cracking temperature to a non-reactive temperature not substantially in excess of 600 F. This latter temperature effectually precludes the liberation of free carbon but yet is sufficiently high to permit of the fractionation of the vapors without resource to additional heat.

More oil is forced'through the coil 31 into the arrester than is necessary to replenish the normal fuel demands of the system, Therefore, in order to take care of this excessive quantity of oil the bottom of the tower 29 is equipped with an outlet line 36, in which is located a pump 37. The latter serving first pipe line 38 and since this oil contains an appreciable quantity of heat it is preferably passed pipe line 23 so as to preheat the oil passing through the pipe line 23. From the heat exchanger 39 the oil which is being forced through the line 38 may then be transferred to a second heat exchanger 40 for delivery to the working tank 32. By passing through the heat exchanger 40 the heat contained in the oil may be advanused to generate steam which may in turn be supplied to the system through the steam line 15. The recycle stock delivered back to the tank'32 may be returned to the pipe line 21 for recirculation through the system by a pipe line 41 which connects the tank '32 with the pipe line 21. The line 21 is valved as at 42 to regulate oil flow therethrough or, if desired, the recycle stock may be totally redelivered to the system through the spray coil 31.

Also, the bottom of the fractionating tower 29 is outlet line 43 which is connected with a pump whereby the recycle stock is forced through the pipe line 9 to the vaporizing bank of tubes 8.

In view of the foregoing it will be seen that the present invention provides for the cracking of oil in the vapor phase and wherein this end is attained with continuous operation. By the employment of the arrester 21 it will be observed that the tarry fractions of the charging stock will be stripped from the latter before such chargvaporized. Also, in

to force the oil through a.

,a gravity offrom 4 to 12 ing stocks reach the vaporizing bank of tubes 8, using for this purpose the heat content of the issuing vapors of the converter. The highly heated cracked vapors issuing directly from the converter, are mixed with a quantity of fresh topped crude, the temperature of which is so regulated bymeans of the heat exchanger 39 that the combined temperatures of the topped crude and issuing converter vapors are such that the tarry mat-' ter in the issuing converter vapors (present on account of the cracking reactions) is condensed and the topped crude is raised to such a temperature that all fractions except tarry matter are p the event the charging oil is cracked by this ,operation, the heavy residual products of such cracking separate from the vapors and drop to the bottom of the heat exchanger 1 or arrester 21. Therefore, at the outlet 25 in the bottorrrfof the arrester the system discharges a heavy pitch-like residue having a gravity of from 4 to 12 Baum. This material is unfit for sale as fuel oil, but in a highly heated condition can be burned at the converter setting. The vapors then pass upwardly and through the arrester and are shock chilled by means of the spray located 100 in the top, their temperature being reduced to a point where further decomposition does not take 1 place and the liquid condensate of the vapors may then be conducted to the fractionating vtower'29.

A certain amount'of cracking of the fresh topped 105 crude may take place on account of the high temperature in the bottom of the arrester. This cracking is immaterial and does not affect detrimentally the operation of the system.

Under the above conditions of operation, the bottom of the fractionating tower 29 will not contain any tarry matter, but will be substantially a clean gas oil of a wide boiling range. Part of this material will be pumped through the economizer 8 into the evaporator 11. As previously stated, this material is practically free from tarry matter and, therefore, it will be possible to operatethe tubes 8 at a fairly high temperature so that the vapors passing therethrough will attain a temperature of I at least 800 to 825 F., thus, permitting of the vaporization of the material under any existing pressure of the evaporator up to substantially pounds per square inch without any substantial deposit from coke. There will be certain heavy'gas oil fractions which under these conditions will not vaporize, but these fractions may be drawn off from the bottom of the evaporator to form a commercial fuel oil having a gravity of between 12 and 20 Baum. 1

The operation above described sets forth par. ticularly the use of topped crude oil as a charging stock. However, should the system be operated on a charging stock consisting of gas oil 35 alone, such gas oil will be drawn from the working tank 32. This gas oil may or may not be preheated and introduced into the issuing vapor line of the converter, where it is used to condense out the tarry substances existing in the issuing n cracked vapo'rs which tarry fractions have been formed on account of the cracking reactions or which may be present for other reasons. Enough charging oil may be pumped in order to cool the issuing vapors to effect the condensation of the tarry products and produce a residuum having Baum. In the case of topped crude operation, if the quantity of topped crude is not sufilcient to cool the issuing vapors to the desired gravity residuum, a small amount of gas oil will be introduced, as shown,

-' the bottom portion of the arrester, by heating this material its cooling power is lessened and,-

therefore, a satisfactory temperature will be at tainecl.

It will be observed that in the above system the heavy tarry fractions will be produced at a point of lowpressure in the system, since the pressure of the arrester will be substantially the same as that of the fractionating tower and, therefore, at a pressure of approximately five pounds per square inch, a low gravity residuum may be produced at a low temperature and with consequent decreased likelihood of coke formation. There will also be a considerable heat saving over earlier systems, by more efficiently utilizing the heat of the converted vapors without wastev and in minimizing the heating of residual oils of an undesirable character in the vaporizing tubes 8.

While we have described what we consider to be the preferred form of the present invention,

zone, heating an elongated confined stream of said vapors to" temperatures not substantially in excess of active vapor phase cracking temperature to vaporize liquid oil entrained in the vapors, increasing the velocity of the dried vapors and heating them to temperatures in excess of 1000 F. to effect the pyrolytic conversion thereof and sharply reducing the temperature of the products of conversion by admixing cool hydrocarbon oil therewith in sufficient quantity to rapidly reduce the temperature of the heated vapors to one below active pyrolytic conversion temperature.

AUDLEY E. HARNSBERGER. CLYDE L. SMITH.

CERTIFlCATE 0F CORRECTION.

Patent No. l, 927, 829.

September 26, 1933 It is hereby certified that the name of the first mentionedpatentee in the grant and in the heading to the printed specificationof the above numbered patent, was erroneously written and printed as "Audiey E. Harnesberger" whereas said name should have been written and printed as "Audley E. Harnsberger" as shown by the records of the case in this office; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.-

Signed and sealed this 28th day of November, A. D. 1933.

(Seal) F. M. Hopkins Acting Commissioner of Patents.

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