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Title:
MECHANICAL TREATMENT SYSTEM FOR SLOP WATER AND METHOD FOR USE OF SAME
Document Type and Number:
WIPO Patent Application WO/2017/007330
Kind Code:
A1
Abstract:
A treatment system (1) for slop water is described, the treatment system (1) comprising : - a decanter (2) including at least an inlet (21) for the slop water which is to be purified and an outlet (22) for a water phase, - a separator (4) connected to the decanter (2) downstream thereof; and - an analyser (3) including an analyser unit (31) placed upstream of the inlet (21) of the decanter (2) of the treatment system (1) for determining the solids and oil content of the slop water. What is characteristic of the treatment system (1) is that the analyser (3) of the treatment system (1) further includes a second analyser unit (32) downstream of the decanter (2) for analysing the water phase coming out therefrom; and that said analysis of said water phase determines: - whether the water phase will be returned for re-purification in the decanter (2); or - whether the water phase will be passed on to the separator (4), and in that case the settings thereof. A method for purifying slop water by the use of said treatment system ( 1) is described as well.

Inventors:
BERGSVIK OLUF (NO)
ÅSLAND GLENN (NO)
TVETERAAS JAN ERIK (NO)
Application Number:
PCT/NO2016/050137
Publication Date:
January 12, 2017
Filing Date:
June 23, 2016
Export Citation:
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Assignee:
SOILTECH AS (NO)
International Classes:
E21B21/06; B01D17/02; B01D21/00; C02F1/38
Foreign References:
DE3322599A11985-01-03
US8834723B12014-09-16
US20140166576A12014-06-19
US6132630A2000-10-17
Attorney, Agent or Firm:
HÅMSØ PATENTBYRÅ ANS (NO)
Download PDF:
Claims:
C l a i m s

1. A treatment system (1) for mechanically purifying slop water, the treatment system (1) comprising :

- a decanter (2) including at least an inlet (21) for the slop water which is to be purified and an outlet (22) for a water phase,

- a separator (4) connected to the decanter (2) downstream thereof; and

- an analyser (3) including a first analyser unit (31) placed upstream of the inlet (21) of the decanter (2) of the treatment system (1) for determining the solids and oil content of the slop water;

c h a r a c t e r i z e d i n that the analyser (3) of the treatment system (1) further includes a second analyser unit (32) downstream of the decanter (2) for analysing the water phase coming out therefrom; and in that said analysis of said water phase determines:

- whether the water phase will be returned for re-purification in the decanter (2); or

- whether the water phase will be passed on to the separator (4), and in that case the settings thereof.

2. The treatment system (1) according to claim 1, wherein the treatment system (1) further includes a treatment device (7) placed between the decanter (2) and the separator (4), for the further removal of particles and oil from the water phase.

3. The treatment system (1) according to claim 2, wherein the treatment device (7) is a filter package.

4. The treatment system (1) according to any one of the preceding claims, wherein the treatment system (1) further includes a further treatment device (8) placed downstream of the separator (4), for the further removal of particles and oil from the water phase.

5. The treatment system (1) according to claim 4, wherein the further treatment device (8) is a filter package.

6. The treatment system (1) according to any one of the preceding claims, wherein the treatment system further includes a desalination unit (9).

7. The treatment system (1) according to claim 6, wherein the desalination unit (9) includes a membrane for reverse osmosis.

8. The treatment system (1) according to any one of the preceding claims, wherein the analyser (3) further includes a third analyser unit (33) downstream of the separator (4).

9. The treatment system (1) according to any one of the preceding claims, wherein the analyser (3) includes a computer system (35) for automatically interpreting analyses from the analyser units (31, 32, 33) and controlling the fluid flow in the treatment system (1).

10. A method for purifying slop water by the use of a treatment system (1) according to claim 1, the method including the following steps:

a) determining the solids and oil content of the slop water in the first analyser unit (31); and

b) carrying the slop water into the decanter (2) in order to at least remove particles, oil and a water phase;

c h a r a c t e r i z e d i n that the method further includes the following steps:

c) analysing the water phase that comes from the decanter (2) in the second analyser unit (32) downstream of the decanter (2); and on the basis of the result of said analysis: either

d) returning the water phase of the decanter (2) to the decanter (2) for re- purification with subsequent repetition of step c); or

e) carrying the water phase of the decanter (2) into the separator (4) in order to at least remove particles, oil and a water phase; and, in that case, setting the separator (4) on the basis of the analytical results from the second analyser unit (32) .

11. The method for purifying slop water according to claim 10, wherein step c) of the method includes determining the residual particle and oil content of the water phase of the decanter (2).

12. The method for purifying slop water according to claim 11, wherein step c) of the method is followed by step d) if the particle content of the water phase of the decanter (2) exceeds a predetermined value; and wherein step c) is followed by step e) if the particle content of the water phase of decanter (2) is lower than or equals the predetermined value.

13. The method for purifying slop water according to any one of claims 10-12, wherein the method further includes the following steps: f) determining the residual particle and oil content of the water phase of the separator (4) in a third analyser unit (33); and

g) if the oil content of the water phase of the separator (4) exceeds a predetermined value: carrying the water phase into the separator (4) again, and then repeating step f) until the oil content of the water phase of the separator (4) is lower than the predetermined value.

14. The method according to any one of claims 10-13, wherein, between steps d) and e), the method includes the further step : h) passing the water phase through a treatment device (7) for the further removal of particles and oil .

15. The method according to any one of claims 13-14, wherein, after step g), the method includes the further step: i) passing the water phase through a further treatment device (8) for the further removal of particles and oil.

16. The method according to any one of claims 10-15, wherein the method further includes the further step: j) passing the water phase through a desalination unit (9).

Description:
MECHANICAL TREATMENT SYSTEM FOR SLOP WATER AND METHOD FOR USE OF SAME

The invention relates to a treatment system for mechanically purifying slop water, the treatment system comprises a decanter which includes at least an inlet for the slop water that is to be purified and an outlet for a water phase, a separator connected to the decanter downstream of the latter, and an analyser which includes an analyser unit placed upstream of the inlet of the decanter of the treatment system for determining the solids and oil content of the slop water. Further, the invention relates to a method for purifying slop water by means of the treatment system according to the invention. More precisely, the invention relates to a treatment system and a method for treating slop water on a drilling device for subsequent discharge to the sea or ground, the method being based exclusively on analyses of the slop water and a series of mechanical purification stages. Accordingly, the method is without the use of chemicals.

By the term "slop water" is meant herein liquid waste that is generated in connection with the recovery of petroleum, for example liquid waste from drilling, production and intervention operations. The contents of the drilling waste vary according to the operation being carried out. The drilling waste may consist of water contaminated with drilling fluid, oil-contaminated water, oil-contaminated brine, slop water, slop water with cement residues, liquid containing particles, liquid from drains and also rainwater, soapy water and similar liquids. The particle content of the liquid drilling waste and its composition may vary greatly. The slop-water treatment system described herein is suited for all the above-mentioned types of liquid waste. It must be understood that the terms "liquid drilling waste" and "slop water" may be used interchangeably herein and cover the great variety of wastewater described above.

The conventional handling of the drilling waste has been to transport the waste to a special location for treatment and destruction, or, alternatively, to inject the waste into a well that has been drilled for this purpose. The challenge with respect to dis- charge to the sea or ground is to achieve a purity that meets the environmental requirements for the emission of oil into water.

Today there are a number of purification processes for handling slop water on a drilling device before subsequent discharge into the sea or ground. Known purification processes include a combination of chemical and mechanical treatment. A typical process would be preparing the slop water by heating and adding a flocculant before carrying it into a decanter in which two, possibly three, phases are separated, the water phase possibly continuing to a separator.

The patent publication US 2014/166576 Al discloses a treatment system composed of a hydrocyclone, membrane systems, decanter and separator.

In the patent publication DE 3322599 Al a treatment unit which collects and treats liquid and sludge-like waste containing mineral oil is disclosed. The treatment unit comprises four purification stages, the first stage of which comprises mechanical separation of the coarsest matter by the use of a shale shaker. In the second stage, oil is separated and water liberated from the sludge in a three-phase decanter. The third stage comprises settling of the last, suspended solids in sedimentation tanks. In a secondary purification stage, an oil-binding additive is used to remove any remaining oil.

A drawback of known treatment processes is that even if they can result in a water phase that satisfies the requirements for emissions of oil into water, they may contain chemical additives, for the emission of which no requirements exist.

Another drawback is that the need for adding flocculation agents, for example, makes it necessary to store chemicals at the site.

Still another drawback of the prior art is so-called secondary waste generated by the use of chemicals, this secondary waste requiring further purification.

A further drawback of the prior art is that in processes in which, in the main, mechanical treatment is used there are often large, space-demanding systems that include sedimentation tanks, for example. This may be impractical, or impossible, to use on installations offshore because of limited space.

Further, in mechanical processes, vibratory-screen separators that may generate some noise and that may be very space-demanding are often used.

There are also known systems using both a decanter and a separator. A know problem with such systems is that the separator clogs up because of too much solid matter or too large particles in the solids of the water phase coming to the separator from the decanter. This problem leads to unwanted down-time of the system for maintenance. A similar problem is known from systems using hydrocyclones and membranes, namely that too great amounts of particles will result in the hydrocyclone or the membrane clogging up.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art.

The object is achieved through the features that are specified in the description below and in the claims that follow.

In the treatment system according to the invention no chemicals are added to the liquid drilling waste, or the slop water. No heating is used either. The method provides for separating the slop water into three distinctive phases: particles, oil and water. The water that is separated has an oil-in-water (OIW) purity that makes discharge into the sea or ground possible. The purity requirements may vary somewhat from country to country, but today the purity requirement for discharge into water or ground in Norway is 30 ppm. The system according to the invention may be adapted for different purity requirements and will preferably produce water which is cleaner than what is required by the emission requirements. For example, the system may produce water with a purity of less than 10 ppm of oil in water, for example 5 ppm of oil in water. In this way, cost-increasing and polluting transport of the slop water is avoided.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments of the invention.

In a first aspect, the invention relates more specifically to a treatment system for mechanically purifying slop water, the treatment system comprising :

- a decanter including at least an inlet for the slop water which is to be purified and an outlet for a water phase,

- a separator connected to the decanter downstream thereof; and

- an analyser including an analyser unit placed upstream of the inlet of the decanter of the treatment system for determining the solids and oil content of the slop water. The treatment system is characterized by the analyser further including a second analyser unit downstream of the decanter for analysing the water phase coming out therefrom and by said analysis of said water phase determining whether the water phase will be returned for re-purification in the decanter or whether it will be passed on to the sepa- rator. If the water phase is passed on to the separator, the analysis of the water phase from the decanter determines the settings of the separator.

A decanter is a centrifuge that separates components of different densities. A decanter can be used to separate, for example, two or three different components from each other, wherein these components may be solids, liquids or gases. In the treatment system according to the invention, the decanter is preferably a three-phase decanter, that is to say a decanter which separates components of three different densities from each other, for example solids, oil and water. An example of a three-phase decanter which can be used in the treatment system according to the invention is the Tri- canter® from the company Flottweg SE.

A separator works in a similar way to the decanter, the separator also being a centrifuge, but, in the main, separators handle liquids and finer solids and work at a higher rate of rotation than a decanter.

In the treatment system according to the invention, the liquid drilling waste, referred to as slop water in what follows, will first be carried into the decanter which separates out the coarsest particulate material, an oil phase and a water phase. The particulate material is carried to a collection receptacle for solids, the oil phase is carried to a collection receptacle for oil and the water phase is analysed to determine the residual amounts of solids and oil therein after the first round in the decanter. A limit on how great an amount of solids can be tolerated in the water phase from the decanter for it to be allowed to be carried directly to the separator has been set in advance. This limit value can be chosen on the basis of which type of separator is part of the system, and which final result is required after the water phase has been passed through the separator. In the treatment system according to the invention, the separator is preferably a three-phase separator, that is to say a separator which is suitable for separating three phases from each other, such as solids and two liquids of different densities.

It is also conceivable that a limit is set on the size of particulate material tolerable in the water phase from the decanter for it to be passed on to the separator.

It is the analyser unit placed between the decanter and the separator that analyses the water phase from the decanter and that thus forms the basis for whether the water phase will be passed on to the separator or back to the decanter for a new round. The analysis carried out in the analyser unit upstream of the decanter forms the basis for the settings of the decanter when new slop water is carried into it.

What is fundamental to the treatment system according to the invention is that there is this analyser unit between the decanter and the separator that determines where the water phase is carried after the decanter and that further also determines the settings of the separator, for the most effective purification possible.

By using this system, a clogging of the separator by too large or too great an amount of solids is avoided, and thereby the whole process can be optimized.

The treatment system according to the invention is a purely mechanical system and therefore no chemicals such as flocculants are used. Because of the optimized procedure of analysis with subsequent settings for the next stage of the purification process, the treatment system will be so effective that even without the use of chemicals the water that comes out of the last purification stage will be so clean that it may be discharged directly into the sea or ground. There are several reasons for it being an advantage not having to use chemicals; firstly, storing chemicals on board the platform is avoided. Secondly, the formation of an intermediate product or secondary waste consisting of flocculants to which both oil and water are bound, which in its turn must be transported to shore for purification, is avoided. Accordingly, as a consequence of not having to have this intermediate product, more clean water will come out of the process, and the residual products, particulate phase and oil phase, will be less voluminous.

The treatment system may further include a treatment device placed between the decanter and the separator for the further removal of particles and oil from the slop water.

Based on the analysis of the water phase coming out of the decanter, it may be appropriate in some cases to direct said water phase into a treatment device placed between the decanter and the separator instead of returning it for another round in the decanter if the analysis does not indicate that the water phase may be carried directly to the separator. The treatment system may be set up with different limit values, so that a solids content, and possibly the particle size, over a certain value indicate(s) return to the decanter, whereas there is then also a fringe range of solids content and/or particle size which indicates that the water phase should instead be directed into a further treatment device between the decanter and the separator. It must be understood that the system may be adapted in such a way that the decision to carry the water phase into the treatment device between the decanter and the separator may also be based on other factors than particle content and particle size, for example oil in water, oil-particle size, heavy metals, minerals and so on. This depends on what type of treatment device is placed between the decanter and separator, and what it is meant to purify the slop water of.

The treatment device may be a filter package, which is a possible embodiment of the treatment system according to the invention. The filter package may typically be arranged to remove a particular fraction of particulate material and maybe also oil or other contaminants in the water.

The treatment system may further include a further treatment device placed downstream of the separator for the further removal of particles and oil from the slop water.

In a manner similar to that of the treatment device between the decanter and the separator, the further treatment device may have been installed to either handle a specific range of particle sizes, purify the water phase of oil or other specific contaminants in the water, or a combination of these.

The further treatment device may be a filter package, which is a possible embodiment of the treatment system according to the invention.

The treatment system may further include a desalination unit. It is conceivable that instead of discharging the purified water directly from the separator, possibly from the further treatment device such as a filter package, into the sea or into the ground, it may be desirable to recycle the purified water for use aboard the installation at sea. If the water should desirably be used for purposes with particular requirements for purity, for example cleaning, personal hygiene or even drinking water, a salinity within given limits is required; for example, ideally, less than 500 ppm for freshwater.

There are various known devices for water desalination, for example devices for distillation, ion exchange or reverse osmosis.

The desalination unit may include a membrane for reverse osmosis. Reverse osmosis is a known method of desalinating water, for example sea water, and will be well suited in the treatment system according to the invention.

The analyser may further include a third analyser unit downstream of the separator. In those cases in which it is considered to discharge the fully purified water directly into the sea or ground, it must first be analysed to find out whether the oil content, for example, is within the allowed limits. There may also be other factors than the oil content that are examined in such an analyser unit. If the oil content or other parameters have been found to exceed the given limit values, the water phase from the separator, possibly from the further treatment device downstream of the separator, may be returned for another round in the separator.

The analyser may include a computer system for automatically interpreting analyses from the analyser units and controlling the fluid flow in the treatment system. The treatment system according to the invention can be automated, fully or partially, so that the different analyser units are connected to each other and to the decanter and the separator, and also the further treatment devices and the desalination unit if included in the system, via a SCADA system. In this way the system may be programmed and adjusted for the slop water on the installation in question.

In a second aspect, the invention relates more specifically to a method for purifying slop water by the use of a treatment system according to a first aspect of the invention, the method including the following steps:

a) determining the solids and oil content in the slop water in the first analyser unit; and

b) carrying the slop water into the decanter in order to at least remove particles, oil and a water phase.

What is characteristic of the method is that it further includes the following steps: c) analysing the water phase that comes out of the decanter in the second analyser unit downstream of the decanter; and on the basis of the result of said analysis: either d) returning the water phase of the decanter to the decanter for re-purification with subsequent repetition of step c); or

e) carrying the water phase of the decanter into the separator in order to at least remove particles, oil and a water phase; and, in that case, setting the separator on the basis of the analytical results from the second analyser unit.

The aim of the method according to the invention is to purify slop water in such a way that at the end of the process, the water that is separated in the purification process is at least so clean that it satisfies the requirement for purity for discharge directly into the sea or into the ground .

This is achieved by the method according to the invention, by thorough and frequent analysis of the water phases coming out of the different purification stages, the decanter and the separator, and by providing for the water phase to be purified mechanically, and without the addition of chemicals, a sufficient number of times for solids to be separated and the oil content of the water getting to be below the given official limit values. Determining the solids and oil content of the slop water in an analyser unit before it is carried into the decanter, makes it possible for the settings of the decanter to be adjusted for the entering material. This makes the purification become more effective. The decanter is particularly well suited for removing the coarsest material. Slop water to be purified in the treatment system may typically contain 0-50 % solids and 0-20 % oil.

Analysing the slop water before it is carried into the decanter may be done continuously if the system is automated, for example. Alternatively, samples may be taken systematically, either manually or automatically, for example at given time intervals or on having passed a given volume of slop water. The frequency of analysis at the different analyser units of the system may be adjusted for the existing needs.

A decanter comprises a bowl and a scroll, wherein these are to be considered as two sleeves placed one inside the other. The bowl and the scroll are arranged to rotate in opposite directions and at different speeds. Both the speed in general and the difference in speed between the bowl and the scroll are of importance for the purification process. They may be set on the basis of the solids content of the slop water. If there is a great amount of particles, it may be advantageous to have a lower speed difference than if there are few particles. In the same way, a lower general speed may be effective with a great proportion of coarse particles, whereas a higher general speed is more effective with finer particles.

Otherwise, the possibilities of setting a decanter are known to a person skilled in the art and will also be described in the user manuals for decanters of known types, for example the Tricanter® from Flottweg SE, and will thus not be described any further herein.

As mentioned, solids, oil and a water phase will come out of the decanter. The solids are carried to a receptacle, or a collection site, for solids, whereas the oil is correspondingly carried to a separate collection receptacle. The separated water phase is analysed in a second analyser unit downstream of the decanter. Here it is determined, on the basis of predetermined criteria, whether the water phase will have to be returned for another round in the decanter or whether it is to be passed on to the separator. Since the composition of this water phase that comes out of the decanter varies, it will be appropriate to adjust the settings of the separator on the basis of the results of the analysis in the second analyser unit. This second analyser unit thus has the effect of the system being optimized by the water phase from the decanter not being passed on, but being returned, if it is not suitable for the separator. Further, the sec- ond analyser unit has the effect, if the water phase is found to be in order for being passed on to the separator, of making the separator be set particularly with a view to the composition of exactly this water phase. In this way, the reliability and effectiveness of the system may be ensured. As an example it may be mentioned that if a water phase with a high solids content is passed on to the separator, there will be a risk of the separator jamming up or becoming plugged up, which will result in a stoppage. This is a relatively common problem with the prior art, which is solved by the treatment system according to the invention.

Step c) of the method may include determining the residual particle and oil content in the water phase of the decanter. The particle and oil content may be two important parameters to determine with a view to the further settings of either the decanter or the separator, according to where the water phase is carried. In the art, one speaks about finding a "cut point" within a suitable area for the next purification stage, the cut point being a measurement of the size and composition of particles in the water phase.

Step c) of the method may be followed by step d) if the particle content of the water phase of the decanter exceeds a predetermined value; or step c) may be followed by step e) if the particle content in the water phase of the decanter is lower than or equal to the predetermined value.

Setting a limit value for particle content is a possible embodiment of the method according to the invention. It is also conceivable that limit values are set for other components in the slop water, or that there are limit values for several components at the same time, so that the water phase that comes out of the decanter must satisfy all of these before it may be passed on to the next purification stage which, in this embodiment, is the separator.

The method may further include the following steps:

f) determining the residual particle and oil content in the water phase of the separator in a third analyser unit; and

g) if the oil content of the water phase of the separator exceeds a predetermined value: carrying the water phase into the separator again, and then repeating step f) until the oil content of the water phase of the separator is lower than the predetermined value.

In one embodiment of the method according to the invention, the separator is the last purification stage before fully purified water is discharged into the sea or ground, pos- sibly is collected. If the water is to be discharged or used for various purposes, it is necessary to check the purity of the water.

Between steps d) and e), the method may include the further step: h) passing the water phase through a treatment device for the further removal of particles and oil.

The method for purifying slop water may further be adapted for the slop water in question by including one or more treatment devices in addition to the decanter and the separator. In one embodiment, a treatment device for removing particles and oil may be included between the decanter and the separator. After an analysis of the water phase from the decanter, it may then be decided whether the water phase is to go back to the decanter, to the separator or to the treatment device between the decanter and the separator before it goes to the separator. The treatment device may be a filter package, for example.

After step g), the method may include the further step: i) passing the water phase through a further treatment device for the further removal of particles and oil.

Yet another further treatment device, for example a filter package, may be included in the treatment system for further purification of the water phase that comes out of the separator.

The method may further include the further step: j) passing the water phase through a desalination unit. If the fully purified water is to be usable for hygienic purposes or even for drinking water, for example, there are also limits for the permitted salinity of the water. For the water to be recycled, for example for use aboard an offshore installation, the water phase that has been fully purified with a view to discharge into the sea or ground may be passed through a desalination unit, for example in the form of reverse-osmosis membranes.

In what follows, examples of preferred embodiments are described, which are visualized in the accompanying drawings in which :

Figure 1 is a flowchart showing a treatment system comprising a decanter and a separator;

Figure 2 is a flowchart showing a treatment system comprising a decanter and a separator and a treatment device between the two;

Figure 3 is a flowchart showing the treatment system of figure 2 including a further treatment device; and Figure 4 is a flowchart showing the treatment system of figure 3 further including a desalination unit.

Figure 1 shows, in the form of a flowchart, how a treatment system 1 according to the invention may be set up in one embodiment. The treatment system 1 comprises three main components, namely a decanter 2, an analyser 3 and a separator 4. The treatment system 1 is suitable for purifying liquid drilling waste or so-called slop water, reference being made to the definition of liquid drilling waste initially in this application. The slop water is carried into the decanter 2 through an inlet 21 after the composition of the slop water has been analysed for particle, oil and water content in a first analyser unit 31 of the analyser 3.

In some cases, if the analysis in the first analyser unit 31 shows that, for example, the particle content of the slop water is so low that the slop water may advantageously be carried directly to the separator 4 of the treatment system 1, this may be done via a bypass 101. In the opposite case, the slop water is carried into the decanter 2 after the settings thereof have been adjusted according to the portions of solids, oil and water contained in the slop water, and also according to the particle size of the solids.

The decanter 2 separates solids, which are carried out of the decanter 2 through an outlet 23 and on to a collection receptacle 5 for solids. Further, the decanter 2 separates oil, which leaves the decanter 2 through an outlet 24 and which is carried to a collection receptacle 6 for oil. The remaining slop water, which has not been separated out as solids or oil, is referred to as the water phase from the decanter 2 and is carried out of the decanter 2 through an outlet 22. This water phase is then analysed in a second analyser unit 32 for residual oil and particle content. If, for example, the residual particle content is higher than a predetermined limit value, the water phase may be returned to the decanter 2 through the return line 102. In the opposite case, the separator 4 will be set on the basis of the analysis of the water phase, and the water phase is carried into the separator 4 via an inlet 41. In this embodiment, the separator 4 is a three-phase separator which can separate three different phases, in this case particles or fines, oil and a water phase. The fines come out of the separator 4 through an outlet 44 and are returned for another round in the decanter 2 via the return line 103. Oil is separated through an outlet 43 and carried to the collection receptacle 6 for oil. The water phase from the separator 4 is separated out via an outlet 42 and is then analysed in a third analyser unit 33.

It must be noted that in those cases in which the water phase from the decanter 2 turns out to be pure enough to make it unnecessary for it to be passed through the separator 4, it may be carried outside the separator 4 in a bypass line 104.

If the analysis of the water phase from the separator 4 in the analyser unit 33 shows that the water is clean enough according to the criteria that have been set, the slop water is considered fully purified and the water phase from the separator may be carried into the sea or ground or to some suitable collecting site 10. In the opposite case, the water phase from the separator 4 not satisfying the purity requirements set, it may be returned for another round in the separator 4 via a return line 105.

The analyser 3 may include a computer system 35 which controls the analyser units

31, 32, 33 and which further provides communication between the analyser units 31,

32, 33, the decanter 2 and the separator 4 in such a way that the settings of the decanter 2 and the separator 4 can be made automatically on the basis of the analytical results from the analyser units 31, 32, 33.

In one embodiment, the treatment system 1 including a number of valves may be controlled in its entirety from a PLC (Programmable Logic Controller) system 36 which may be monitored via the computer system 35.

Figure 2 shows the same system as figure 1, with the addition of a treatment device 7, for example a filter package. After an analysis of the water phase from the decanter 2 in the second analyser unit 32, the water phase may be carried into the treatment device 7 via an inlet 71. In the figure, the treatment device 7 is shown as two parallel filter packages, and the inlet 71 comprises two inlets. In the filter packages, any remaining larger particles and possibly also oil may be removed . In the embodiment shown, solids and oil will stay behind in the filter package, whereas the water phase is passed on to the separator 4 via the line 106. The treatment device 7 constitutes an extra purification stage that the water phase from the decanter 2 may be brought to bypass if it is not necessary or desired in a given case. In another exemplary embodiment, it is conceivable that the filter package is self-cleaning and that there is an outlet for solids and/or oil.

In figure 3, the treatment system 1 of figure 2 has been expanded with a further treatment device 8. The further treatment device 8 is provided with an inlet 81. In the embodiment shown, the further treatment device 8, too, is shown as a filter package with two parallel filters. The water phase that comes out of the further treatment device 8 is carried via the line 107 to a fourth analyser unit 34. If the analysis in the analyser unit 34 shows that the requirements for purity of the water phase are not met, the water phase will be returned via the return line 105 to the separator 4 or via the return line 105 and the bypass line 104 for another round in the further treatment device 8. Like the treatment device 7, the further treatment device 8, too, may be made to be self-cleaning. In such an embodiment, there will be a further outlet for solids and oil, for example in the form of a return line to the decanter.

In figure 4, an embodiment of the treatment system 1 that is further provided with a desalination unit 9 is shown. The desalination unit 9 may, for example, be a unit for reverse osmosis. Even though the desalination unit 9 is shown here in a set-up including the two treatment devices 7, 8, it must be understood that the desalination unit 9 could just as well have been shown in an embodiment without one or both of these treatment devices 7, 8. At the fourth analyser unit 34, the salinity of the water is analysed in addition to the other factors like oil content, for example. On the basis of said analysis, the water will then either be returned to the separator 4 or the filter package 8, be passed on to the desalination unit 9 or be carried out of the treatment system to be used anew. If the water is carried into the desalination unit 9, it will then be analysed in a fifth analyser unit 37 at the outlet thereof, to determine whether the water now has the desired salinity or whether it will have to be returned to the desalination unit 9 once more.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art will be able to construct many alternative embodiments without departing from the scope of the attached claims. In the claims, reference numbers in parentheses are not to be regarded as restrictive. The use of the verb "to comprise" and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.