GB2145730A

GB2145730A - Process and apparatus for simultaneously dewatering, desalting and deasphalting a mixture of hydrocarbons

Info

Publication number: GB2145730A
Application number: GB08419884A
Authority: GB
Inventors: Jean Louis Dubarry; Emmanuel Garland
Original assignee: Societe National Elf Aquitaine
Current assignee: Societe National Elf Aquitaine
Priority date: 1983-08-08
Filing date: 1984-08-03
Publication date: 1985-04-03
Also published as: FR2550545B1; JPS6060188A; GB8419884D0; FR2550545A1

Abstract

Water and a precipitant (e.g. gasoline) are added to a hydrocarbon mixture, and the mixture containing the additives is introduced into a gravimetric separator 15 in which it separates into three superposed phases: a lower phase consisting essentially of salty water, an upper phase consisting essentially of the mixture of hydrocarbons which has been purified and the precipitant, and an intermediate phase essentially consisting of asphaltenes and water; the three phases are removed separately via lines 3, 4, 5 respectively and the precipitant is separated in distillation apparatus 28 from the mixture of hydrocarbons which has thus been dewatered, desalted and deasphalted. <IMAGE>

Description

SPECIFICATION Process and apparatus for simultaneously dewatering, desalting and deasphalting a mixture of hydrocarbons Field of the invention The present invention relates to the treatment of a mixture of hydrocarbons, particularly crude oil from which it is desired to remove all or a part of the water, salts and asphaltenes. This permits the purified hydrocarbons to be conveyed or discharged under better conditions.

Prior art Until now, the dewatering and the desalting of a mixture of hydrocarbons and its deasphalting have always been designed independently. There are numerous processes permitting dewatering and desalting at the same time, as well as processes for deasphalting, but these two operations are never combined.

The mixtures of unpurified hydrocarbons, and particularly heavy crude oils, have a density and a viscosity which are very high. Because of this is necessary to "flux" them, that is to say to add light hydrocarbons to them in order to be able to dewater and desaltthem. However, even afterfluxing, it is often difficult to dewaterthese crudes properly, because the asphaltenes which they contain tend to trap water. When a light flux is employed, there is an additional risk of precipitation of a part of the asphaltenes with formation of a stable and thick interface. Finally, the crude, as it leaves the desalting line, upstream of the distillation column which is normally employed to regenerate the flux, presents problems during transfer on account of its high viscosity.

These difficulties are, at least partly, attributable to the asphaltenes the removal of which is desirable for dewatering.

Summary ofthe invention The aim of the invention is to dewater, dealt and reduce the asphaltene content of crude hydrocarbons in a single operation with, as favourable consequences, an improvement in the rheological behavior of the mixture of purified hydrocarbons.

The subject of the invention is a process for carrying out simultaneously, in a single operation, the dewatering, desalting and deasphalting of a mixture of hydrocarbons, particularly crudes and residues, in which water and a precipitant are added to the mixture, the mixture containing the additives is introduced into a gravimetric separator in which is separates into three superposed phases: a lower phase consisting essentially of salty water, an upper phase consisting essentially of a mixture of purified hydrocarbons and flux, and an intermediate phase essentially consisting of asphaltenes and water, and three phases are extracted separately and the precipitant is separated from the mixture of hydrocarbons which has thus been dewatered, desalted and deasphalted.

It is generally advantageous to employ a light gasoline as precipitant. Similarly, particularly advantageous results are obtained by adding a deemulsifier to the hydrocarbon mixture before treatment.

To use the process according to the invention it is generally preferable to carry out the separation of the precipitant by a quick distillation, and to carry out the treatment under a pressure which is greater than atmospheric pressure, particularly under compressed nitrogen.

The asphaltenes may be easily recovered by a quick distillation of the intermediate phase extracted from the separator. The gravimetric separation is promoted by the presence of a highivoltage electrical field. It is generally possible to carry out the whole treatment according to the process of the invention at a temperature of the order of 90 to 1 1 O"C, which is a temperature that is much lower than that normally employed for dewatering crudes according to conventional processes which call for temperatures of the order of 130 to 1500C.

Another subject of the invention is a purifier apparatus for extracting water, salt and asphaltenes from a mixture of hydrocarbons in accordance with the process of the invention. This apparatus essentially consists of preferably vertical receptacle incorporating a first pipework for delivering the mixture to be treated and a second pipeworkforthe removal of salty water, opening into the base of the receptacle, a third pipeworkfor removing the purified mixture of hydrocarbons, opening into the top of the receptacle and a fourth pipework for removing a mixture of water and asphaltenes.

Such apparatus preferably comprises, between the third and fourth pipework, at leat two conductive plates placed apart, each connected respectively to one of the poles of a source of high-voltage electric current.

An apparatus according to the invention advantageously comprises means for heating the mixture which is being treated, as well as means for applying and maintaining pressure.

For flexible and steady operation, an apparatus according to the invention incorporates means detecting the location of the layer of mixture of water and asphaltene relative to the entry of the fourth pipework.

Brief description of the drawing The invention will be understood better from the reading of some detailed examples of implementation of the process of the invention, and from the examination of the attached drawing which shows, by way of example, an apparatus according to the invention inserted into a plant for treating crude hydrocarbons.

Detailed description The plant shown diagrammatically in the drawing essentially comprises a tank 11 containing the mixture of crude hydrocarbons to be treated. A pump 12 conveys this crude mixture via a pipework 13 to a first pipework 2 for delivering the mixture to be treated into a purifier apparatus according to the invention 15. This pipework 13 incorporates means of heating shown diagrammatically by a broken line which heat the cride mixture, stored at approximately 70"C in the tank 11, up to 100"C at the entry of the pipework 2 for delivery to the apparatus according to the invention.

At 16, de-emulsifier is injected into the pipework 13 and at 17 fresh water is injected into this same pipework. Between the pipeworks 16 and 17, light gasoline stored in a tank 18 is injected into the same pipework 13. A pump 19 makes is possible to inject the required quantities of light gasoline into the crude, Valves 20, 21 and 22 permit some sections of the pipework 13to be isolated at will.

The purifier apparatus 15, according to the invention, consists essentially to a verticaly receptacle 1, lagged and incorporating conventional means of heating 8. Into the base of the receptacle 1 opens a first pipework for delivering the mixture to be treated 2, and a second pipework for the removal of salty water 3. Into the top of the receptacle 1 opens a third pipework 4 for removing the purified mixture of hydrocarbon. This pipework 4 conveys the dewatered, desalted and deasphalted hydrocarbon mixture to a quick distillation apparatus 23 of the "flash" type, esentially consisting of a plateless distillation column, operating by expansion the incorporating means of heating. From this distillation apparatus 23 light gasoline recovered from the hydrocarbon mixture which has been treated is extracted at the top, by a pipework 24.The light gasoline recovered in this way is conveyed to the tank 18, in order to recycled. The purified hydrocarbon mixture is withdrawn, through a pipework 25, from the lower part of the distillation apparatus 23. Inside the purifier apparatus 15 are arranged two conductive plates 6,7 separated from each other and connected, in both cases, respectively to the poles of a source of high-voltage electric current, not shown.

The two plates 6, 7 are arranged approximately at the upper third of the receptacle 1, in the liquid phase formed essentially by the purified hydrocarbon mixture and the light gasoline employed as flux.

At the lower third of the receptacle 1 there opens a fourth pipework 5 for removing the mixtire of water and asphalteneforming an intermediate phase between the upper phase consisting of purified hydrocarbons and the lower phase consisting substantially of salty water. Conventional detecting means 10 make it possible to monitor the location of the layer of mixture of water and asphaltene which forms the interface, relative to the entry of the fourth pipework 5.These detecting means 10 control, through the intermediacy of a relay 26, the operation or the stoppage of a pump 27 which takes in, through the pipework 5, the mixture of asphaltene and water and delivers ittoa quick distillation apparatus 28 of a similar structure so that of the distillation apparatus 23, already described, from which the asphaltenes are removed by a lower pipework 29, while the light gasoline which is partly present in the mixture of asphaltene and water is removed at the top of the distillation apparatus 28 via pipework 30 and, after being cooled at 31, is either recovered or recycled via pipework 32 conveying the light gasoline thus recoverd to the tank 18. Naturally, the pipeworks 5 and 29 are lagged and incorporate means for heating, in order to prevent the asphaltenes from setting.

Such a plant may be employed for a continous proessing of crude hydrocarbons. The residence time in the apparatus is approximately 10 minutes, the electric field of the order of 12 kV and it is preferable to maintain a nitrogen pressure of 7 bars which is injected into the pipework 4 via a pipework 9, as shown in the diagram.

A plant such as this is employed, for example, with effluents heated to 70"C before mixing, a holding time in the separator apparatus 15 of approximately 15 minutes, a nitrogen pressure in this same apparatus of 3 bars gauge, a temperature in the distiller 23 of 100"C under atmospheric pressure and a temperature of approximately 150"C in the asphaltenes distiller 28 at a very slight over-pressure and an electric field between the grids 6 and 7 of approximately 1000 volts per centimeter separation.

Example I The crude oil "Mormora mare", of Italian origin, with a density at 15"C of 1019 kg)m3 and a viscosity of 100,000 cSt at 20"C is employed as a mixture of crude hydrocarbons to be treated.

To 100 volumes of this crude, containing 1 volume of water, and at a flow rate of 4 liters/hour are added 25 volumes of washing water at a flow rate of 1 liter/hour, 300 volumes of a light gasoline (15-80 C) at a flow rate of 12 litreslhour and 0.01 volume of de-emulsifier of the type sold under the trade name Visco Q 3 E by the company called Nalco, at a flow rate of 0.016 liter/hour.

This mixture is injected via pipework 2 into the apparatus 15, where it is treated at 110"C.

21.2 volumes of salty water are extracted through the pipework 3, at a flow rate of approximately 0.85 liter/hour.

From the apparatus 28 are extracted, after distillation, on the one hand a mixture of 9.5 volumes of asphaltene at a flow rate of 0.37 liter/hour through the pipework 5 and 3.5 volumes of water at a flow rate of 0.141iterfhour, through the pipework 29. 46.3 volumes of light gasoline are recovered at a flow rate of 1.3 liters hourthrough the pipework 30.

At the outlet of the distiller 23 are recovered, through pipework 24,254 volumes of light gasoline at a flow rate of 10.17 liters/hour, mixed with 0.3 volume of water at a flow rate of 0.012 liter/hour.

Finally, through the pipework 25 are recovered 90 volumesofdeasphalted, desalted and dewatered crude at a flow rate of 3.6 liters/hour, its viscosity being 440 cSt at 200C.

Example 2 Crude oil called "Boscan", originating from Venezuela, is employed in this example; its density at 15"C is 998 kg)m3. Its viscosity at 20"C is 300,000 cSt.

It contains approximately 11% by weight of asphaltene.

To 100 volumes of this crude are added 25 volumes of washing water and 250 volumes of light gasoline (15-80"C) and this mixture is injected, without a de-emulsifier, via the pipework 2, into the treatment apparatus where it is treated for 15 minutes at 90"C.

17.7 volumes of salty water are removed via pipework 3. 45 volumes of light gasoline and 7.2 volumes of water are recovered via pipework 30. 25 volumes of crude asphaltene are removed via pipework 29.

205 volumes of light gasoline and 0.1 volume of water are recovered via pipework 24, while via pipework 25 are recovered 75 volumes of crude deasphalted, desalted and dewatered hydrocarbons the viscosity of which is 725 cSt at 20"C and the asphaltene content is 1% by weight.

To evaluate the effect of the temperature of processing in apparatus 15, the same treatment as in Example 1 is carried out, and using the same products, but at 900C instead of 110"C.

After treatment, the water content of the crude which was 0.8% before treatment, drops to 0.05% after treatment at 900C and to below 0.03% after treatment at 11 00C.

The asphaltene content, initially 12% by weight, is reduced to 1.2% by treatment at 90"C and to 0.6% by treatment at 110 C.

The viscosity at 20"C, which was 100,000 cSt for the crude before treatment, drops to 725 cSt after treatment at 90"C and to 440 cSt after treatment at 1100C.

In all of the above, reference has been made to fresh water, but it is clearly understood that other suitable waters can be employed, such as sea water, oilfield water, and the like.

Claims

1. A process for simutaneously carrying out, in a single operation, the dewatering, desalting and deasphalting of a mixture of hydrocarbons, particularly crudes and residues, to which water, a precipitant and a de-emulsifier have been added, in which the mixture containing the additives is introduced into the base of a gravimetric separator where it separates countercurrentwise into three superposed phases: a lower phase consisting essentially of salty water, an upper phase consisting essentially of the purified mixture of hydrocarbons and precipitant, and an intermediate phase essentially consisting of asphaltenes and water, the three phases are removed separately and the precipitant is separated from the hydrocarbon mixture which is thus dewatered, desalted and deasphalted.

2. The process according to Claim 1, characterised in that a light gasoline is employed as precipi tant.

3. The process according to one of Claims 1 and 2, characterised in that the gravimetric separation is supplemented by the action of a high-voltage electric field produced between two electrodes arranged in, and traversed by, the upper phase.

4. A purifier apparatus for removing water, salt and asphaltenes from a mixture of hydrocarbons characterised in that it essentially consists of a receptacle (1) incorporating a first pipework for delivering the mixture to be treated (2) and a second pipework for removing salty water (3), both opening into the base of the receptacle, a third pipework for removing the purified hydrocarbon mixture (4) opening into the top of the receptacle and a fourth pipeworkfor removing a mixture of water and asphaltenes (5), opening into the receptacle between the second and third pipeworks (3,4).

5. The apparatus according to Claim 4, characterised in that it comprises, between the third (4) and fourth (5) pipeworks (4, 5) at least two conductive plates (6, 7), arranged horizontally, separated, each connected respectively to one of the poles of a source of high-voltage electric current.

6. The apparatus according to one of Claims 4 and 5, characterised in that it incorporates means for heating (8) the mixture being treated.

7. The apparatus according to one of Claims 4to 6, characterised in that it incorporates means for placing and maintaining the mixture being treated under pressure (9).

8. The apparatus according to Claim 4, in which the receptacle 1 is vertical.

9. A process for simultaneously dewatering, desalting and deasphalting of a mixture of hydrocarbons substantially as hereinbefore described with reference to the accompanying drawing.

10. A purifier apparatus for removing water, salt and asphaltenes from a mixture of hydrocarbons substantially as hereinbefore described with reference to the accompanying drawing.