US3798153A

US3798153A - Crude oil processing

Info

Publication number: US3798153A
Application number: US00326616A
Authority: US
Inventors: J Arndt; W Ebert
Original assignee: Chevron Research and Technology Co
Current assignee: Chevron USA Inc
Priority date: 1973-01-26
Filing date: 1973-01-26
Publication date: 1974-03-19
Anticipated expiration: 1991-03-19

Abstract

IN A PROCESS WHICH COMPRISES HEATING, DESALTING AND THEN FURTHER HEATING HYDROCARBONACEOUS OIL USING HEAT EXCHANGERS AND A DESALTER, AN IMPROVEMENT IS MADE WHICHP COMPRISES: (A) DESALTING THE OIL TO OBTAIN DESALTED OIL; (B) INJECTING A HOT FLUID INTO THE DESALTED OIL, SAID HOT FLUID BEING AT A TEMPERATURE HIGHER THAN THE DESALT OIL; AND (C) FLASHING THE DESALTED OIL BEFORE FURTHER HEATING OF THE DESALTED OIL IN ANY HEAT EXCHANGER. PREFERABLY, THE HOT FLUID INJECTED INTO THE DESALTED OIL IS A HOT DISTILLATE WITHDRAWN FROM THE CRUDE OIL DISTILLATION COLUMN LOCATED DOWNSTREAM OF THE FLASHING STEP. THE HOT DISTILLATE SERVES TO AMELIORATE POSSIBLE FOAMING IN THE FLASH DRUM BY LOWERING THE VISCOSITY OF THE DESALTED OIL THROUGH RAISING THE OVER-ALL TEMPERATURE AND THROUGH THE LOWER VISCOSITY OF THE DISTILLATE COMPARED TO THE CRUDE OIL AT A GIVEN TEMPERATURE.

Description

CRUDE OIL PROCESSING Filed Jan. 26, 19713 bmw.

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\ l:o M0310 United States Patent O 3,798,153 CRUDE OIL PROCESSING John H. Arndt, Jr., Berkeley, and Wayne A. Ebert, Dublin, Calif., assignors to Chevron Research Company, San Francisco, Calif.

Filed Jan. 26, 1973, Ser. No. 326,616 Int. Cl. Cg 17/00, 33/00 U.S. Cl. 208-48 AA 9 Claims ABSTRACT OF THE DISCLOSURE In a process which comprises heating, desalting and then further heating hydrocarbonaceous oil using heat exchangers and a desalter, an improvement is made which comprises: (a) desalting the oil to obtain desalted oil; (1b) injecting a hot iiuid into the desalted oil, said hot fluid being at a temperature higher than the desalted oil; and (c) flashing the desalted oil before further heating of the desalted oil in any heat exchanger. Preferably, the hot iuid injected into the desalted oil is a hot dis tillate withdrawn from the crude oil distillation column located downstream of the flashing step. The hot distillate serves to ameliorate possible foaming in the flash drum by lowering the viscosity of the desalted oil through raising the over-all temperature and through the lower viscosity of the distillate compared to the crude oil at a given temperature.

BACKGROUND OF THE INVENTION The present invention relates to reducing fouling in heaters, particularly heat exchangers, used to heat oil.

The term fouling is used herein to mean deposition of material on heat transfer surfaces, usually with subsequent reduction in heat transfer coefficient, and usually also with an increase in pressure drop.

Essentially all oil refineries have crude oil distillation units. The crude oil distillation units basically consist of crude oil preheat exchangers, a desalter, a furnace, and a crude oil distillation column. The present invention is particularly concerned with reducing fouling in the crude oil preheat exchangers, although the process of the present invention can be applied to other heat exchanger surfaces where desalting is involved.

The basic function of a crude oil distillation unit is to split crude oil into diiferent `'boiling-range fractions of the crude oil for further-downstream processing or for iinal use. To carry out splitting of the crude oil into various fractions fby distillation, the crude oil must be heated to a high temperature to allow substantial vaporization as required for the crude oil distillation.

The heating of the crude oil ahead of the crude oil distillation column is generally carried out by heat exchange with hot products from the crude oil distillation column, and finally by heating in a furnace. The heat exchangers are usually shell and tube exchangers, with the crude oil usually flowing through the tubes and taking up heat from hot products flow-ing through the exchanger outside of the tubes; that is, through the shell side of the exchanger. A simplified crude-oil heating train is shown on page 38 of R. J. Hengstebecks Petroleum Process, McGraw-Hill, 1959.

Before the crude oil completes the flow through the heat-exchange train, it is usually subjected to desalting. Desalting is applied to remove brine from the crude oil. It is accomplished by mixing Water With the crude oil whereby the water unites with the brine. The aqueous (brinewater) phase is separated from the oil by settling; in most modern plants removal of water droplets from the oil is aided by electrical means.

The brine which is separated from the oil contains ICC salts such as sodium chloride, calcium salts, magnesium salts, etc.

Desalting of crude oil is described in more detail at page 265 of W. L. Nelsons Petroleum Reiinery Engineering, fourth edition, McGraw-Hill. As shown by data given on page 94 of Nelsons book, some crude oils are so low in salt content that desalting is not needed. But this is the exception, rather than the rule, and desalting nearly always is applied.

Also, before the crude oil completes the heating ahead of the crude oil distillation column, it is frequently ashed.

'Ihe word dashed is used to mean the vaporization of part of the oil mixture by reduction of the pressure on the oil mixture. Thus, in many crude oil units, after the oil is heated to about 350 to 550 F., it is flashed into a flash drum. The iiash drum removes light components, such as Water and low-boiling hydrocarbons, from the oil so that the iiow through the final heating, the furnace, is reduced. The overhead from the flash drum is introduced usually as a vapor to the crude-oil distillation column. The bottoms are heated in the furnace and then fed to the crude-oil distillation column.

Many crude-oil units have a desalter but no flashing step. In either case, the desalting step is typically at a temperature of about 250 F., that is, considerably below a typical ashing step temperature (assuming a iiashing step is employed at all). Desalting is preferably carried out at the low temperautre, because: (1) the separation of the :brine from the oil is usually more eiiicient at the lower temperature, particularly -if electrical means are used to aid in the separation; and (2) it is usually felt desirable from the standpoint of reduced heat-exchange fouling to reduce the salts before reaching a temperature above 300 \F. Flashing is typically done at a higher temperature, because light components are removed more effectively by ashing olf from the majority of the crude oil at higher temperatures, compared to lower temperatures.

Therefore, in the past, heat exchangers have been used after desalting and before flashing in order to increase the temperature from the desalting temperature to a more desirable ashing temperature (or to a higher temperature to prepare the oil for further heating or introduction to the distillation column).

SUMMARY `OF THE INVENTION `In accordance with the present invention, in a process which comprises heating and desalting and then further heating hydrocarbonaceous oil using heat exchangers and a desalter, the improvement is made which comprises:

(a) Desalting the oil to obtain desalted oil;

(b) Injecting a hot fluid into the desalted oil, said hot iiuid being at a temperature higher than the desalted oil, and

(c) Flashing the desalted oil before further heating of the desalted oil in any heat exchanger.

The present invention is based further on an advantageous means to raise the temperature and especially to lower the viscosity of the desalted oil between the desalting step and the ashing step, but yet Without using any heat exchanger between these two steps; namely, the present invention uses direct heating by injection of a hot fluid between the desalting step and the flashing step.

In desalting, as in other processing, eiciency is, of course, not achieved. Thus, there are at least small amounts of brine left in the oil after the desalting step. AIt is theorized that upon ashing the oil from the desalting step, remaining water-that is, a substantial portion,

liashed from the crude oil, and salts precipitate out as rather sizable aggregates, similar to dirt particles. If the water is left in the oil, the salt also stays dissolved in the oil by means of the water which is carried with the oil. It is theorized that the salt left in the oil in this form tends to act as a cementing means to result in very tenacious deposits to heat-exchanger surfaces, such :as the inside of heat-exchanger tube walls. On the other hand, it is theo- ',rized that :in the process lof the present invention, when the water is substantially hashed out of the oil the salts precipitate out as aggregates, which aggregates in turn do not deposit extremely tenaciously upon the heat-exchange surfaces or cause extremely tenacious deposits on heatexchange surfaces.

Thus, it is seen that the present invention is considerably different from prior art methods of attack, which in many instances were directed to ehicient desalting per se, so as to remove the salt constituents from oil and thereby improve downstream operations. In fact, the data which we have obtained and analyzed show that in some instances extremely efficient desalting per se can increase heat-exchanger fouling rather than decrease heat-exchanger fouling. It is theorized that the increased fouling resulting from more ehicient desalting per se is caused by the fact that the desalting substantially dehydrates the oil in its ehicient separation of the aqueous phase from the oil phase, with the result that little aqueous phase is left to maintain the remaining trace Iamounts of salts in solution. Thus, those trace amounts of salts left in the oil deposit tenaciously or cause tenacious deposits on the walls of the exchanger tubes as the temperature of the crude oil is increased when howing through the downstream exchangers.

lConnected with this, it should be pointed out that `a number of salts exhibit inverse solubility as, for example, calcium sulfate, which is progressively less soluble at higher temperatures, so that as temperatures are increased it tends toward depositing out from solution in trace amounts of water in the oil. In addition, Ias the temperature is raised, water tends to dissolve in oil and/or vaporize so that less liquid-phase water is left to hold salts in solution.

Also, the process of the present invention can be contrasted to those prior art processes which suggest simple addition of an Iadditive for reducing heat-exchanger fouling. For example, U.S. Pat. 3,390,073, entitled Hydrocarbon Additive for Heat Exchanger Anti-Pouling, is directed to the addition of an anti-foulant additive at points such as downstream of a crude-oil desalter but ahead of crude oil preheat exchangers'.

In the process of the present invention the crude oil desalting step is followed by a hashing step before passing the crude oil through any heat exchanger. The hash temperature should be selected at about the lowest temperature where crude oil can be hashed without foam problems. Foaming tends to be reduced if the crude oil is at a low viscosity. Thus, this is one of the factors which has caused the hashing step in the past to be carried out at relatively high temperatures compared to the desalting step, as viscosity is lower at higher temperatures. However, in the process of the present invention it is desired to operate at about the lowest temperature for the hash without going into the substantial-foaming-temperature regime. In the present invention, relatively low tempera.- tures are desired for the hashing step because the hashing step immediately follows the desalting step, and it is generally desirable to carry out desalting at a low temperature, compared to the nal temperature of the crude oil before the crude oil is fed to the crude-oil distillation column.

However, in the process of the present invention the hash temperature should be suhciently high so that the vapor pressure of steam is suhiciently high to result in at least 75% of the free water hashing off or vaporizing from the crude oil in the hash d-rum. Alternatively, this may be phrased in terms of pressure in the hashing step or hash drum; the pressure in the hash drum preferably is below the vapor pressure of free water at the temperature in the hash drum. Free water refers to that water over and above the Water which is soluble in the oil as a true solution.

Injection of a hot Ihuid in accordance with the present invention allows obtaining of higher temperatures for the feed to the hash drum, reduces the viscosity of the feed to the flash drum and, hence, reduces the foaming tendency of the crude oil hashed into the hash drum. The hot huid which is injected into the desalted oil is advantageously a hot oil which can be obtained from within the over-all rehnery complex. A particularly preferred hot oil for raising the temperature of the desalted crude oil is -a crude oil distillate withdrawn from the crude oil distillation column which follows downstream of the hashing step. Preferably the distillate has a viscosity at about 300 F. which is lower than the viscosity of the desalted crude oilat 300 F. Use of such distillate helps to reduce foaming in the hash drum after the desalter by raising the temperature of the desalted crude oil and by lowering the viscosity of the crude oil, compared to the desalted crude oil without distillate added at a given temperature, such at 300 F.

An alternate, preferred means for raising the temperature of the desalted crude oil is a hot crude oil recycle stream obtained from the effluent from Ia heat exchanger downstream of the hashing step. Use of this stream has an advantage over the distillate stream in that the distillate stream use result in a higher vapor liquid loading of the furnace and crude oil distillation column and a higher withdrawal of the ydistillate from the distillation column. However, use of the distillate has the advantage of an inherent ability to cut viscosity of the desalted crude oil. Also, the use of the injection of a hot oil into the desalted crude oil is most desirable when the crude oil feedstock is a heavy oil, and in the ease of a heavy oil, the loading of the crude oil distillation column is less than in the case of a lighter oil. Hence, the use of a recycle distillate stream usually does not cause overloading of the crude oil distillation column at the time when the distillate recycle is most needed, namely during the processing or relatively heavy, high-viscosity crude oils, which tend to cause a foaming problem in the hash drum due to their relatively high viscosity.

Preferably the temperature of the hot injection huid, such as hot oil or hot steam, is at least F. above the temperature of the desalted oil.

As indicated above, the present invention is particularly advantageously applied to the processing of relatively heavy crude oils which, due to their relatively high viscosities, have a greater tendency to cause foaming problems in the hashing step than do lighter, less viscous crude oils. According to a preferred embodiment of the present invention, the crude oil feed has a gravity greater than 36 API, the desalting is carried out at a temperature between about 200 and 300 F., and huid of suhiciently hot temperature, and in suhicient amount, is injected into the desalted oil to raise the temperature of the desalted oil at least 10 F. and to a temperature between 250 and 390 F. It should, of course, be understood that the term hot as used herein means that the hot huid which is injected has a temperature greater than that of the stream into which the hot huid is injected.

According to a specic embodiment of the present invention, a process is provided for reducing the fouling of crude-oil distillation unit preheat exchangers downstream of a desalting step, which process comprises: (a) heating feed crude oil to a temperature between -450 F. by passing the oil through heat exchanger tubes at a pressure between 20 and 500 p.s.i.g. and transferring heat from a hot huid across the tube walls to said oil; (b) removing salts from the oil in a desalter by contacting the oil with water and then separating the oil from the water et a pressure between 2Q and V500 psig. and a tem;

.5 perature between 150-450 F.; (c) injecting a hot fluid into the desalted oil, said hot fluid being at a temperature higher than the desalted oil; (d) flashing olf remaining Water from the oil, before further heating in any heat exchangers, by reducing the pressure below the vapor pressure of free water at the temperature of the ashing step; and (e) then further heating the oil to a temperature above the flashing temperature and between about 350- 900 F. by passing the oil through heat-exchange tubes and transferring heat from a hot uid across the heatexchange-tube walls to the oil.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flow diagram illustrating a preferred embodiment of the present invention.

DETAlLED DESCRIPTION F THE DRAWING Referring now more particularly to the drawing, crude oil feed is introduced to the process via line 1. Water is injected into the crude oil feed via line 2, and then the mixture is pumped via pump 3 and line 4 to heat exchanger 5. The Water injection can be omitted, but usually is desirable to help reduce fouling in heat exchanger 5.

Heat exchanger 5 represents what is usually a series of heat exchangers.

The preheated crude oil feed is passed via line 6 to desalter 7 at a temperature of about 250-325 F. The desalter is used to remove the brine from the crude oil in accordance with Well-known desalting techniques. The separation of the aqueous brine phase from the oil is frequently aided by electrical means so that a substantially water-free oil is obtained after the desalting step. The separated brine phase is withdrawn from the bottom of the desalter via line 8.

In prior art processes, the substantially water-free oil, particularly as obtained after highly efficient electn'cal desalting, frequently causes severe exchanger [heat-transfer-surface fouling downstream of the desalter. However, in the process of the present invention, heat exchangers are not used immediately after the oil is withdrawn from the desalter.

However, it is desired to raise the temperature of the desalted oil before hashing the oil into flash drum 12. This is particularly true in the case of relatively heavy crude oils having a specific gravity above about 361 API (0.845 specific gravity), because these heavy, viscous crude oils tend to cause severe foaming or emulsion problems upon ashing the oil at temperatures typically used in the desalting step. Prior processes have generally simply contended with high heat-exchanger fouling between thc desalting step and the flashing step, if it was necessary to increase the temperature of the crude oil between the desalting step and the flashing step. Attempts to reduce the fouling in the heat exchanger between the desalting and flashing steps were made in the form of the use of anti-fouling agents, but these anti-fouling agents usually attained only a small level of success in reducing the fouling. The injection of water after the desalter has also been suggested to reduce the fouling in thejheat exchanger typically used between the desalting and ashing steps, but this step has the disadvantage of increasing water removal problems and increasing the volume of vapors which must be flashed in -ash drum 12. Also, the use of water injection results in the consumption of additional heat energy to vaporize the water, and water has a relatively high heat vaporization compared to that for other materials such as hydrocarbons. In the process of the present invention, the problem of high heat exchanger fouling between the desalting step and the ashing step in a crude oil distillation unit is overcome but yet without using a water injection step downstream of the desalter, and thus avoiding the attendant problems in such water injection. l t

Referring again in particular to the drawing, a hot desalter 7 via line 9. The hot fluid can be chosen from a variety of hot fluids available in a refinery complex, such as hot oil or steam. In any case, the hot fluid must, of course, be at a temperature which is above that of the desalted oil leaving the desalter. As shown in the drawing, the hot iluid which is used is a crude oil distillate stream withdrawn from the crude oil distillation column. An alternate, preferred source of hot fluid for heating the desalted oil is indicated by line 26: a recycle stream of crude oil withdrawn from a point after the crude oil has been heated in heat exchangers downstream of flash drum 12.

The hot iluid introduced into the desalted crude oil raises the temperature of the desalted crude oil by 10 F. or more, for example, from about 280 to about 320 F., and hence reduces the viscosity of the desalted crude oil. The heated, desalted crude oil is introduced to hash drum 12 via line 11.

Upon flashing, the temperature of the desalted crude oil is reduced, for example, from about 320 to 300 F. Vaporized hydrocarbons and remaining small amounts of water are withdrawn via line 13 from the top of the flash drum. This vapor stream is typically introduced to crude oil distillation column 23 at the flash zone of the distillation column. The flash zone is the point or region of the distillation column to which the main crude oil feed is introduced to the column via line 20. Substantially dehydrated liquid oil is withdrawn from ash drum 12 via line 14 and pumped by pump 15, and then passed in line 16 to heat exchanger 17.

lHeat exchanger 17 schematically represents what is usually against a series of heat exchangers, just as heat exchanger 5 is a schematic representation. The heating of the crude oil for both

heat exchangers

5 and 17 is typically accomplished -by a hot iluid passed through the shell side of the heat exchangers with the crude oil owing through the tubes in the heat exchangers. The hot fluid passing through

exchangers

17 and 5 is indicated respectively by

lines

27 and 28.

Heat exchanger fouling is usually not as great as problem in heat exchanger 17 as in the case of heat exchangers located between the desalting and llashing steps, possibly because heat exchangers between the desalting and flashing steps can incur fouling due to salt depositing out from trace amounts .of Water remaining in the desalted oil withdrawn from desalter 7.

Heat exchanger 17 usually heats the crude oil to about 400-550 F., and then oil is heated further in furnace 19 so that a partially vaporized stream is withdrawn from furnace 19 at a temperature of about 650 F.

The partially vaporized crude oil stream is introduced via line 20 to distillation column 23 for fractionation into various distillate fractions, which are withdrawn from the distillation column as schematically indicated by

lines

22, 24 and 25.

The heavy part of the crude oil is withdrawn from the distillation column as reduced crude oil via line 21.

v Further description of the drawing and preferred embodiments of the present invention are given in Example 2.

EXAMPLE l Data were obtained from an operation (designated as PN). The crude oil heating train in the PN operation consisted of a rst heat exchange, desalting, further heat exchange (second heat exchange), flashing, still further heat exchange (third heat exchange), furnace heating, and then introduction to a crude oil distillation column. The water used for desalting in this operation was zeolitesoftened water. The connate water in the crude oil was basically sea water, having large amounts of sodium chloride and only relatively small amounts of calcium salts. In this operation the data which were obtained and analyzed showed severe fouling for the second heat exchange, that is, fouling in the heat exchanger between fluid is injected into the-desalted crude oil, which leaves 75. the desalting and the flashing steps. The deposits were very tenacious and could be successfully cleaned from the heat-exchange surface (i.e., in this instance, inside of the exchanger tubes) only by vigorous means such as reamingy out the deposits from the exchanger tubes.

The main salt component carried over by the entrained water from the desalter in the subject operation was, of course, expected to be sodium chloride. Metals analysis of the desalted crude oil confirmed that the sodium content (1 ppm.) was greater than the calcium content (0.4 p.p.m.). Analysis of the unwashed fouling deposit, however, showed that the calcium content was two orders of magnitude higher than the sodium content, and that the main constituent was CaSO4-an inverse solubility salt. The principal salt components in the fouling deposit were:

Weight percent Na 0.121 Ca t 16.8 Cl 0.08 S04 45.2

The presence of iron sulfate and iron sulfide was also noted.

The above salt analysis supports other data which we have analyzed indicating that substantial fouling occurs after the desalting step when the crude oil is heating prior to being subjected to a flashing step. It is theorized that the fouling is caused or connected to precipitation of inverse-solubility salts from continuing liquid water droplets; that is, entrained ne water droplets or the like remaining in trace amounts after the desalting step. As stated before, the inverse-solubility salts, such as calcium, have decreased solubility in water as temperature is increased.

Contrasted to the severe fouling in the second heat exchange, the fouling in the third heat exchange, that is, the heat exchange after flashing, was very low, specilically, lower by a factor of at least 10. Of tcourse, the salts which were present in the oil leaving the second heat exchange are still present in the oil after the flashing step, as the salts are not volatile. However, it is believed, in view of the data which have been analyzed, that the salts are in a much less harmful form after the flashing; perhaps because of the removal of remaining water and resultant precipitation of the salts in the flashingA stepas aggregates such as dirt particles. It should be mentioned that the term removal of the remaining water by Hashing does not mean that all of the remaining water is removed as, of course, the water sets up an equilibrium with the oil and, also, even equilibrium is not reached 100% completely, and there are some ineciencies in vapor liquid separation.

EXAMPLE 2 The following example is based on a processdesign utilizing the process of the present invention.

80,000 b.p.d. of a heavy Arabian crude oil having a gravity of 27 API and a viscosity of 3.1 cen'tistokes (cs.) at 250 F. are preheated to 300 F. using a heat exchanger such as indicated by heat exchanger 5 in thev drawing. The preheated crude oil is introduced to an electrical desalter operating at a total pressure of 225 p.s.i.g. and a temperature of about 295 F. An aqueous brine phase is withdrawn from the desalter, and a desalted crude oil having about 0.5 pound of residual water (including about 0.25 pound of free water) per 100 pounds of oil is withdrawn from the top of the desalter. The free water contains from about 300 to 3000= p.p.'m. salts, such as sodium chloride, calcium salts and magnesium salts. A hot diesel fraction is withdrawn from the crude oil distillation column, and a portion of this hot diesel fraction, in the amount of 5000 b.p.d., is passed as indicated by line to the outlet line from the desalter. The temperature of the hot diesel oil is 520 F., so that upon injection into the desalted crude oil the temperature of the resulting mixture, which is .made up and then further heating hydrocarbonaceous oil using heat mainly of the desalted crude oil, is raised 20 F., that is from 295 to 315 F. The portion of the hot diesel oil fraction which is not recycled for use as hot oil injection is steam stripped and then withdrawn as a product diesel oil fraction for marketing or for further processing in the refinery complex, as, for example, by catalytically hydrocracking to obtain gasoline products. The position of withdrawal of the hot diesel oil from the downstream crude oil distillation column is about 10 trays above the feed point (ash zone) of the distillation column. A

According to a preferred embodiment of the process of the present invention the hot injection fluid is withd rawn from the crude oil distillation column at a point at Ileast two trays (or their equivalent) above the column ilash zone and at or below a pumparound heat exchange loop used for the crude oil distillation column. Use of such a liquid distillate stream is advantageous for several reasons. The distillate has a lower viscosity than, say, the crude oil recycle shown in line 26. The lower viscosity helps lower pumping costs in pump 15 and also helps reduce foaming tendencies in the flash drum. Because pump 15 usually has a high head, it is 'very advantageous to minimize vpumping requirements in pump 15- Also, the diesel cut or other distillate cut WithdnaWn from approximately below or at the bottom of the pumparound loop is a thermally efficient stream to use compared to a distillate stream withdrawn from above the pumparound. The energy put into the recycle diesel stream to vaporize the diesel, at the approximately 650 F. ash zone temperature for the distillation column, is recovered with high eiiiciency by the pumparound. The pumparound abstracts heat traveling up the column and transfers the heat typically to crude oil feed. Abstraction of heat further up the distillation column is not as efficient.

In the drawing, the distillate is shown as withdrawn at the bottom of pumparound loop 29. ln pumparound loop 29, hot diesel oil cut withdrawn from the column via line 29 is passed via 29a through exchanger 30 and then back to the column via 2911. Heat exchanger 30 usually is a part of the heat exchange shown schematically by

Vheat exchangers

5 and 17. Thus, typically whole crude oil is heated by flowing, as schematically indicated by line 31, through exchanger 30.

. There may be more than one pumparound loop for the crude oil distillation column. It is preferred to withdraw the hot distillate, used for injection downstream of the desalter, below a pumparound and at a position along the column where the liquid temperature is at least F. above the desalter temperature.

, Referring again specically to this example, the desalted oil Illas a viscosity of 2.2 cs. at 295 F., whereas after injection of the 5000 b.p.d. of hot crude oil distillate the viscosity at 310 F. for the resulting mixture is 1.8 cs. This reduction of viscosity reduces the foaming or emulsion problems upon flashing the desalted crude oil into ash drum 12. The temperature resulting upon flashing into flash drum l12 is 300 F.

The vapor portion ofthe flashed crude oil and also the vaporized residual water which was in the desalted oil is withdrawn from the top of the ash drum, as indicated by line 13, and then fed to the flash zone ofthe distillation column. vSubstantially dehydrated crude oil is withdrawn from the bottom of the flash drum and passed through furtherh'eat exchangers, where the'temperature of the crude oil is raised from 300 4to about 510 F.

The crude oil'is heated further in furnace 19, so that upon ashing into distillation column 23 the temperature in the distillatiori'column Hash zone is 640 F. Distillation is carried out in the distillation column according to wellknown techniques, and the hot distillate injection fraction, that is, the hot diesel oil, is withdrawn as a distilled fraction of the crude oil via

lines

29 and 24, with a 5000 b.p.d..portion of the hot diesel oil being recycled for injection via line 10 as described above.

What is claimed is:

1. In a process which comprises heating and desalting exchangers and a desalter, the improvement which comprises (a) desalting the oil to obtain desalted oil, and then, prior to any further heating of the oil in any heat exchanger,

(b) injecting a hot fluid into the desalted oil, said hot fluid being at a temperature higher than the desalted oil, and then,

(c) ashing the desalted oil before further heating of the desalted oil in any heat exchanger.

2. A process in accordance with claim 1 wherein said hot Huid is a hot oil.

3. A process in accordance with claim 1 wherein the crude oil is fed to a distillation column downstream of the flashing step and a hot distillate stream withdrawn from the distillation column is injected into the desalted oil as said hot fluid.

4. A process in accordance with claim 1 wherein said hot fluid is a hot crude oil recycle stream obtained from the eiuent of a heat exchanger downstream of the flashing step.

5. A process in accordance with claim 1 wherein the oil is substantially dehydrated in the flashing step by ashing the oil into a flash drum at a pressure below the vapor pressure of free water at the temperature of the liquid in the bottom part of the ash drum.

6. A process in accordance with claim 1 wherein the oil is a whole crude petroleum oil.

7. A process in accordance With claim 1 wherein the crude oil has a gravity greater than about 36 API; the desalting is carried out a-t la temperature between about 200 and 300 F.; and suicient hot uid is injected into the desalted oil to raise the temperature of 4the desalted oil at least 10 F. and to a temperature between 250 and 390 F.

8. A process in accordance with claim 3 wherein the distillate withdrawn from the distillation column has a lower viscosity at 300 F. than the desalted crude oil has at 300 F.

9. A process in accordance with claim 3 wherein the distillation column has a pumparound heat exchange loop and the distillate is withdrawn from a point at least two trays above the column ash zone and at or below a purnparound loop.

References Cited UNITED STATES PATENTS 3,565,791 2/1971 Urquhart et al 208-187 FOREIGN PATENTS 645,072 1/ 1948 'Great Britain 208-187 DELBERT E. GANTZ, Primary Examiner J. M. NELSON, Assistant Examiner U.S. Cl. X.R.

gygo C y UNITED STATESv PATENT OFFICE CERTIFICATE OF- CORRECTION Patent No. 3,798,153 Dated March 19 1971+ gInvent:ot'(s) ,Imm E 62nd; ,In and Emme Ehen:

It is certified that error appears .in the above-identified patent Zand that said Letters Patent are hereby corrected as shown below:

Col. 2, line 29, "temperautre" should read tenperature.

Col. 1%, line 23, "such at" should read --such as-.

Col. 1+, line 29 'tresult" should read --results-G.

Col. 6, line 4D, "great as" should read --great a-.

Col. 7, line 75 to Col. 8, lines l-2 "made up and then further heating hydrocarbonaceous oil using heat mainly" should read --made up mainly.

Claim l, Col. 9, lines l-2 "desalting exchangers" should read --desalting and then further heating hydrocarbonaceous oil using heat exchangers.

Signed and sealed this 8th day of October 1974.

(SEAL) Attest:

AMcmf M. GIBSON' JR. c. MARSHALL DANN Attesting Officer 1 Commissioner of Patents