US3160578A - Submerged combustion distillation - Google Patents

Description

United States Patent SUBMERGEB CGWUSTIQN BESTELATi-GN Arthur L. Saxton, Warren Township, Somerset County, Harold N. Weinberg, East Brunswick, and Edward E. Higgins, Chatham, NHL, assignors to Esso Research and Engineering ompany, a corporation of Delaware Filed Dec. 12, 196%, Ser. No. 75,283 8 Qiaims. (3. 2-034l) The invention relates to an improved distillation methad for fractionating petroleum oils. More specifically the invention relates to a novel method for producing asphalts from asphalt-containing crudes.

Distillation is one of the chief methods for fractionating petroleum oils. The basic distillation concept is to charge the petroleum oil, crude, etc. into a distillation column and supply heat to the system by either heating the feed, the bottoms or the bottoms recycle by means of indirect heat exchangers or furnaces. The cost of heating the system is high and represents a major portion of the operating expenses of any distillation unit. it is, therefore, desirable to provide heat to a distillation zone with the least amount of expense and at the highest efdciency possible. The instant invention ers such a process wherein high heating eihciency is obtained.

Additionally the instant invention affords a method whe ein cut points which nomally would require subatrnospheric operating conditions may be effected at atmospheric pressure. Also the instant invention by virtue of the above permits investment and operating economics over conventional heating methods.

It is Well known that asphalt is a major sour e of material for road construction for it provides adequate roads at economical prices. Aside from its use as a roadbuilding material, asphalt finds use in house construction for waterproofing, tile cements, shingles, linoleum backing, and caulking compounds. Furthermore, it constitutes the basic binder for such diverse products as coal briquettes, paints, expansion joint fillers and as an adhesive to name only a few of its myriad of applications. The advantage of providing low cost methods to produce asphalt are thus readily apparent from the market avaflable to this material.

In the past, two methods have predominated in the manufacture of asphalt. One is steam distillation at atmospheric pressure in a batch or continuous operation. This method is somewhat limited inuse, for it is relatively slow and frequently leads to incipient cracking, especially with high boiling asphalt crudes. The second method is a vacuum distillation process comprising two ipe still distillation units. In the first pipe still, which is operated under atmospheric pressure, the asphaltic crude is distilled to separate therefrom the lighter constituents such as naphtha, kerosene, heating oil and gas oil, The residual material is sent to the second pipe still unit wherein it is distilled under a vacuum to separate the heavy gas oil from the asphaltic constituents. Both units require substantial heat inputs. This process is adequate for the production of asphalts but because the second stage must be operated under a vacuum, equipment cost is substantially increased and the operating costs are extremely high.

It is an object of the instant invention to provide an improved method for fractionating petroleum feeds by distillation.

It is also an object of the instant invention to provide a method whereby cutpoints may be obtained by distillation at atmospheric pressure which heretofore required operating under a vacuum.

t is a further object of this invention to provide a method for more efficiently supplying heat to a distillation step.

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Furthermore, it is an object of the invention to provide a method for producing asphalt in a more economical manner.

Briefly, the invention in its broadest form relates to supplying heat to a distillation zone by submerged combustion. Basically, submerged combustion is combusting a mixture of fuel and air and releasing tie flue gas therefrom directly into the liquid to be heated, at bottoms fraction in the distillation zone or a bottoms recycle stream. The high temperature flue gas is discharged below the surface of the liquid and passes upwardly through the liquid and the distillation zone. The direct contact between the hot fiue gas and the liquid and the violent agitation caused thereby effects unusually high heat transfer rates and thermal efhciency is or better.

in regard to the recovery of high cut-point material, such as asphalt, there has been developed an integrated system whereby the feed is preheated with overhead fractions from within the system to form a gaseous, lowboiling fraction and a residuum which is subsequently heated directly by submerged combustion. In this process the crude, after preheating in the manner discussed in more detail hereinafter, is introduced into a flashing zone to remove the light constituents, such as naphtha and other low boiling materials. The reduced crude is then directed to a submerged combustion zone where a mixture of fuel and air is burned and the combustion products released below the surface of the liquid in the combustion zone. vapor overhead comprising combustion products and vaporized components of the reduced crude is then employed to preheat the crude thereby resulting in the condensation of the vaporized components of the reduced crude and allowing separation thereof from the combusti n products. The overhead from the flash zone may likewise be used to preheat the crude.

It is apparent that this method has economical advantages, for it provides a more efficient heating system, high cut points without the use of a vacuum, and eliminates the more costly equipment necessary for vacuum separation.

Other objects and advantages of the instant invention will be apparent from the more detailed description of the invention which follows.

FIGURE 1 is a schematic diagram of the preferred embodiment of the instant invention.

FIGURE 2 is a schematic diagram of another embodiment of the instant invention.

Referring to FEGURE 1 there is illustrated an improved process for producing asphalt from an asphaltcontaining crude and the preferred method of the instant invention. Feed, such as a Tia Juana medium crude, is obtained from a suitable source and directed through line 1 into preheater 2, a heat-exchanger of conventional design. Stream 3, which will be discussed hereinafter in more detail, is used as the heating medium in preheater 2. The crude passes from preheater 2 through line 4 into a second preheater 5, which is a heat-exchanger of any conventional design. Stream 6, which will be discussed hereinafter in more detail, is employed as the heating medium in preheater 5.

tream 7 directs the crude, which has now been heated to a temperature in the range of about 450 to 650 F., to a flash zone 8 wherein the naphtha, light ends and middle distillates are flashed off overhead and removed from the fiash zone by line 3. The cut-point of the materials flashed off in zone 3 will be a function of the temperature of stream 7 entering this zone. As it is preferred that all the middle distillates be flashed and recovered in line 3, it is preferred that stream 7 be heated to a temperature in the range of 600 to 650 F., thus providing a cut-point suficiently high to flash off most of the middle distillates. Flash zone 8 is normally operated at approximately atmospheric pressure, though pressures in the range of 5 to 25 p.s.i.g. may be employed.

Flash zone 8 may be merely a tank wherein stream 7 is discharged for flashing. On the other hand it may be an atmospheric pipe still wherein trays and pumparounds are provided to effect additional separation of the flashed material. The former apparatus is obviously the cheaper one and is preferred if it is unnecessary to effect such additional fractionation of the flashed material.

The overhead stream 3 from the flash zone is directed to preheater 2 wherein it is condensed by resultant heat transfer to the crude in line 1. The condensed overhead is recovered inline 13 for use as desired.

The residue from flash zone 8 is passed via line 9 to submerged combustion zone 10, which may be of a similar construction to Zone 8 with the addition of combustion zone 16. Zone 10 is operated at pressures within the range of about 0 to p.s.i.g. The operating temperature in zone 10 will be in the range of about 650 to 950 F., preferably 700 to 800 F. depending on the cut-point desired. Generally it is desired to merely remove the gas oil fraction of the crude in the overhead from zone 10.

The liquid level of the bottoms in zone 10 is indicated at 14. Below this level there is located a combustion zone 16 wherein fuel from line 11 is ignited in the presence of an oxygen-containing gas, such as air, from line 12. The combustion products, i.e., flue gas, from the combustion Zone 16 pass into and upwardly through the liquid bottoms causing direct heat exchange therewith and violent agitation of the liquid. Combustion zone 16 may be any apparatus suitable to effect this combustion and release of combustion products below the level of a liquid. Many such types of apparatus are well known and any would be suitable to effect the improvements of the instant invention. Fuels suitable for employment in zone 16 would be heavy or light hydrocarbon fuel oil or any single gaseous hydrocarbon or mixture of gaseous hydrocarbons. The particular fuel employed, however, is not critical to the instant process.

The use of the submerged combustion step has the effect of flashing the hydrocarbon stream under a partial vacuum and cut points may be obtained which heretofore would require subatmospheric distillation and equipment suitable therefor. This may readily be seen by a more detailed examination of the circumstances. It is well known that the total pressure of a mixture of gases is the sum of the individual partial pressures. Thus the pressure in zone 10 is the sum of the partial pressures exerted by the flue gas and the hydrocarbon vapors caused by heating. Therefore, if zone 10 is at atmospheric pressure, the partial pressure of the hydrocarbon vapors will be equal to the total system pressure multiplied by their mole fraction in the vapors. Grdinarily, the hydrocarbon partial pressure will be in the range of l to 10 p.s.i.a. It is thus apparent that submerged combustion will have the effect of permitting separations which would otherwise have to be conducted in a vacuum flash or distillation Zone which would require equipment capable of withstanding subatmospheric operating conditions. Such equipment is far more expensive to construct and operate than equipment suitable for atmospheric operating conditions.

The overhead 6, which is a mixture of flue gas and vaporized hydrocarbons from the reduced crude, is directed to preheater 5. Stream 6 will generally be at a temperature in the range of about 700 to 800 F. and preferably contain those hydrocarbons boiling between 600 F. and 1100 F. However, it may contain hydrocarbons boiling in any range between 350 and 1200 F. In preheater 5 heat exchange occurs which causes the condensation of the hydrocarbons which were vaporized from the reduced crude and were taken off in stream 6, thereby allowing an easy separation of these hydrocarbons from the flue gas in separator 18. The flue gas is withdrawn in gaseous form by line 19 while the condensed hydrocarbons are withdrawn through line 20. If desired a portion of these condensed hydrocarbons may be recycled to zone 10.

The bottoms from zone 10 is withdrawn via line 17 and is the recovered asphalt which may be used as desired. The heat which it contains may be utilized by contacting it in heat-exchange relationship with the crude employed as feed in the process.

It has been found that the volume of the flue gas vapors released by the burner 16 is not always suflicient to reduce the partial pressure of the hydrocarbons so as to permit stripping the reduced crude to asphalt. To effect this the burner must be over-fired which results in a general over-heating of the system which is undesirable because of the possibility of cracking, coking, and the need for more expensive materials of construction. It has been discovered that this additional heat required may be removed by injecting water via line 18 into zone 10 below the liquid level. The water absorbs the additional heat and is vaporized to steam which has the ancillary effect of producing more stripping vapors. Therefore, water injection produces additionally required stripping vapors with a minimum expenditure for fuel. Any known liquid injection apparatus would be adequate to effect the advantages of this process modification. For the above reasons the use of stream 18 is a preferred embodiment of the instant invention when extremely high cut points are required.

FIGURE 2 represents another embodiment of the instant invention. The process is basically the same as that shown in FIGURE 1 with the exception that submerged combustion zone 10 is replaced by atmospheric pipe still 30 and reboiler zone 40. Stream 9 from flash zone 8, as shown in FIGURE 1, is directed to atmospheric pipe still 30. Still 30 is operated at a temperature in the range of about 650 to 800 F., so the overhead therefrom will have a cut point in the range of about 600 to 900 F. depending on the partial pressure of flue gas entering via line 35 and on whether or not extraneous stripping gas, such as steam, in introduced through conduit 44. Other fractions, such as a heavy gas oil fraction, etc., may be withdrawn, if desired, as side streams. The bottoms stream 31, which will be at a temperature in the range of about 650 to 800 F., is directed to reboiler zone 40 which contains a submerged combustion unit 32 which may be similar in all respects to burner 16 discussed hereinbefore in relation to FIGURE 1. Fuel and an oxygen containing gas may be supplied thereto in the manner discussed hereinbefore by lines 33 and 34. Zone 40 employs operating conditions essentially the same as that of zone 10 discussed hercinbefore.

The bottoms from reboiler zone 40, which will be at a temperature in the range of about 700 to 900 F., is withdrawn via line 37 and a portion thereof recycled to supply additional heat to still 30 by means of lines 38 and 9. The remainder is withdrawn for use as desired, possibly as an asphalt fraction. A portion of'the overhead 35 from zone 40 may be directed back to still 30 and is introduced therein below the liquid level of the bottoms. The direct contacting of the bottoms in zone 30 with stream 35, which is a mixture of combus tion products and vaporized hydrocarbons, assists in the effective separation of material in that zone. A portion of stream 35 is taken off by line 36 and passed to preheater 5 in FIGURE 1 where it is condensed and subsequently separated in separator 18 into the condensed hydrocarbons and flue gas in the manner discussed hereinbefore.

The overhead 39 from pipe still 30 will contain flue gas'from stream 35 and vaporized hydrocarbons from the reduced crude. The mixture 39 is directed to a condenser 60 wherein the hydrocarbon constituents are condensed and the mixture passed by line 41 to separator 50 where the flue gas is separated from the condensed hydrocarthrough line 43 and a reflux stream which is returned to pipe still through line 42. The coolant material in condenser 60 is preferably the crude to be treated in the process and appropriately this would be done after the crude has passed through preheater 2 (shown in FIGURE 1), but before passing into preheater 5 (shown in FIG- URE 1).

As in submerged combustion zone 16 discussed hereinbefore water may be injected via line 45 into reboiler zone below the liquid level. The advantages obtained thereby are substantially the same as those obtained in zone 16.

It is apparent that the sumberged combustion distillation methods discussed hereinahove have wide applicability to the fractionation of petroleum oils or other streams which are present in any petroleum refinery. For example, it may be employed in combination catalytic cracking unit fractionation to permit'handling additional reduced crude, spent caustic and acid sludge incineration,

and tank farm heating or distillation tower reboiling using a hot oil stream.

What is claimed is:

1. In a process to recover an asphalt from a whole crude the steps comprising preheating said crude to a temperature in the range of about 450 to 650 F., passing said crude to a flash separation zone to form a gaseous overhead fraction containing those hydrocarbon constituents boiling below about 450 F. and a liquid reduced crude, withdrawing said overhead fraction from said flash separation zone and contacting said fraction in heat-exchange relationship with said crude to assist preheating thereof, withdrawing said reduced crude from said flash separation zone, passing said reduced crude to a heated separation zone wherein a second gaseous fraction containing hydrocarbons boiling below about 800 F. and a liquid asphalt fraction are formed, heating said separation zone by releasing flue gas from a submerged combustion burner directly into the liquid bottom fraction wherein water is injected into said separation zone below the liquid level of the asphalt fraction, withdrawing overhead from said separation zone a gaseous stream comprising flue gas and said second gaseous fraction and contacting in heat-exchange relationship said gaseous stream with said whole crude to preheat said whole crude and withdrawing from said separation zone said liquid bottom fraction. I

2. The process of claim 1 wherein said second gaseous fraction is condensed during said contacting with the whole crude and separated from said flue gas in a second separation zone.

3. The process of claim 1 wherein said flash zone is maintained at a pressure of about 5-25 p.s.i.g.

4. A process for segregating a hydrocarbon stream in a distillation zone into an overhead gaseous stream and a bottoms liquid stream which comprises combusting a fuel in a combustion zone submerged in the hydrocarbon in the presence of oxygen to form a flue gas and releasing said flue gas directly into said bottoms liquid to provide the heat for the distillation, said liquid being at about atmospheric pressure, and injecting water into said bottoms liquid stream in said distillation zone to control the temperature of distillation and to provide stripping vapors for carrying out the distillation.

5. A process for recovering an asphalt fraction from a whole crude which comprises the steps of preheating said crude to a temperature in the range of 450-650 F., passing said crude to a flash zone to form a gaseous overhead fraction containing those hydrocarbon constitu ents boiling below about 450 F. and a liquid reduced crude, withdrawing said overhead fraction from said separation zone and contacting said fraction in heat exchange relationship with said whole crude to assist preheating thereof, withdrawing said reduced crude from said flash zone, passing said reduced crude to a heated separation zone wherein a second gaseous fraction containing hydrocarbons boiling below about 800 F. and a liquid asphalt fraction are separated, heating said separation zone by releasing flue gas from a submerged combustion burner directly into the liquid reduced crude and injecting water into said separation zone below the liquid level of the reduced crude to control the temperature of the combustion and to provide stripping gas for said separation zone, withdrawing overhead from said separation zone a gaseous stream comprising flue gas and said second gaseous fraction andcontacting in heat exchange relationship said gaseous stream with said whole crude to preheat said whole crude and withdrawing from said separation zone said liquid asphalt fraction.

6. A process for recovering an asphalt fraction from a whole crude which comprises preheating said crude to a temperature in the range of 450-650 F., passing said crude to a flash zone to separate a gaseous overhead fraction containing those hydrocarbon constituents boiling below about 450 F. and liquid reduced crude, withdrawing said overhead fraction from said separation zone and contacting said fraction in heat exchange relationship with said whole crude to provide preheat for said crude, withdrawing said reduced crude from said flash zone, passing said reduced crude to an atmospheric pipe still, the bottoms from said pipe still are passed to a reboiler wherein flue gas is introduced into said bottoms directly from a submerged combustion burner in said reboiler, water is added to said bottoms to control the temperature and to provide stripping gas, separating overhead a stream of flue gas, steam and vaporized hydrocarbons, a portion of said overhead stream being recycled to said pipe still and introduced into said bottoms in said pipe still to provide heat for carrying out distillation in said pipe still and to provide stripping gas.

7. The process of claim 6 wherein additional heat is added to said pipe still by passing a portion of the hot bottoms from the reboiler to said pipe still.

8. A process for distilling a high boiling hydrocarbon fraction which comprises heating said fraction in a distillation zone, providing heat for said zone by combusting a fuel in the presence of oxygen in a combustion zone submerged in said hydrocarbon fraction, adding water to said liquid hydrocarbon fraction in said distillation zone to control the temperature of distillation, prevent cracking' of the hydrocarbons, and to provide additional stripping gas, and separating overhead a light fraction containing vaporous hydrocarbons, flue gas and stream, and a heavy liquid bottoms product.

References Cited in the file of this patent UNITED STATES PATENTS 7 1,375,245 Averill Apr. 19, 1921 1,585,224 Alexander May 18, 1926 1,673,238 Godsey June 12, 1928 1,842,756 Hill Jan. 26, 1932 1,898,168 Belden Feb. 21, 1933 2,113,635 Tiddy Apr. 12, 1938 2,738,313 Miller Mar. 13, 1956

Claims (1)

1. IN A PROCESS TO RECOVER AN ASPHALT FROM A WHOLE CRUDE THE STEPS COMPRISING PREHEATING SAID CRUDE TO A TEMPERATURE IN THE RANGE OF ABOUT 450* TO 650* F., PASSING SAID CRUDE TO A FLASH SEPARATION ZONE TO FORM A GASEOUS OVERHEAD FRACTION CONTAINING THOSE HYDROCARBON CONSTITUENTS BOILING BELOW ABOUT 450*F. AND A LIQUID REDUCED CRUDE, WITHDRAWING SAID OVERHEAD FRACTION FROM SAID FLASH SEPARATION ZONE AND CONTACTING SAID FRACTION IN HEAT-EXCHANGE RELATIONSHIP WITH SAID CRUDE TO ASSIST PREHEATING THEREOF, WITHDRAWING SAID REDUCED CRUDE FROM SAID FLASH SEPARATION ZONE, PASSING SAID REDUCED CRUDE TO A HEATED SEPARATION ZONE WHEREIN A SECOND GASEOUS FRACTION CONTAINING HYDROCARBONS BOILING BELOW ABOUT 800*F. AND A LIQUID ASPHALT FRACTION ARE FORMED, HEATING SAID SEPARATION ZONE BY RELEASING FLUE GAS FROM SUBMERGED COMBUSTION BURNER DIRECTLY INTO THE LIQUID BOTTOM FRACTION WHEREIN WATER IS INJECTED INTO SAID SEPARATION ZONE BELOW THE LIQUID LEVEL OF THE ASPHALT FRACTION, WITHDRAWING OVERHEAD FROM SAID SEPARATION ZONE A GASEOUS STREAM COMPRISING FLUE GAS AND SAID SECOND GASEOUS FRACTION AND CONTACTING IN HEAT-EXCHANGE RELATIONSHIP SAID GASEOUS STREAM WITH SAID WHOLE CRUDE TO PREHEAT SAID WHOLE CRUDE AND WITHDRAWING FROM SAID SEPARATION ZONE SAID LIQUID BOTTOM FRACTION.

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