GB2510781A - Selective gas stripping of a volatile phase contained in an emulsion, the continuous phase of which is less volatile - Google Patents

Abstract

The present invention relates to a process for removing a dispersed phase of an emulsion (1, 12), characterized in that it comprises a step that aims to subject said emulsion to a gas (19) stripping (18) carried out under temperature and pressure conditions lower than the conditions for boiling the liquid of the dispersed phase, and in which said gas (19) is chosen so that the dispersed phase has a volatility and an affinity with this gas greater than that of the continuous phase of said emulsion.

Description

SELECTIVE GAS STRIPPING OF A VOLATILE PHASE CONTAINED IN AN

EMULSION, THE CONTINUOUS PHASE OF WJ-HCH IS LESS VOLATILE The present invention relates to a process for removing a dispersed phase of an emulsion.

An emulsion is a mixture of at least two non-miscible liquid phases, at least a first phase being dispersed in the second phase, in general in the form of droplets.

The first phase forms a so-called dispersed or discontinuous phase and the second phase forms a so-called continuous phase. Each phase may evidently be a liquid phase or a product or mixture of products.

In the present application, the term emulsion is to be construed in its broad accepted meaning without taking into consideration dispersion characteristics such as droplet size, etc. Emulsions can be formed and be present on numerous occasions whether or not they are desired.

Particular mention can be made of the wastewater treatment sector where oily type particles may be found in suspension in water.

Mention can also be made of the petroleum industry in which treated flows may frequently contain products non-miscible with each other and are likely to form separate phases. From the extraction and refining of crude oil and natural gas up until their conversion into different chemical products, it is thus possible to obtain emulsions whether or not with intent.

It is frequent in particular during crude oil extraction simultaneously to extract water mixed with the hydrocarbons, notably during oil drilling at sea. Water also has high salinity which is harmful for most subsequent operations. Pumping force may lead to dispersion of water in the hydrocarbon phase. In such cases the formed emulsion is obviously involuntary and non-desired, and this aqueous phase must be depleted as much as possible.

It is also frequent to wash hydrocarbon phases with an aqueous phase, in particular to extract a constituent that is at least partly miscible therewith e.g. light hydrocarbons or alcohols, in particular methanol, Washing may then cause the formation of a water-in-hydrocarbon phase emulsion or conversely. In this case, the emulsion formed is intended but only temporarily and it may be necessary to deplete the dispersed phase to obtain a purified continuous phase and/or to recover the dispersed phase.

Mention can also be made of chemical industries using products obtained by emulsion reactions, and in particular emulsion polymerisation in which it may be required subsequently to deplete one of the emulsion phases to recover the synthesized product.

There are numerous processes allowing different compounds to be separated from one another, in particular for such purposes of purification, enriching or fractionating of products or mixtures of products.

These separation processes infer ti/ia comprise distillation, settling, adsorption on solid adsorbent beds, extraction, stripping processes, etc. In general, a separation process is based on a difference in one or more physicochemical properties of the compounds to be separated and makes use of this difference to cause the separating thereof For example the differences may be differences in boiling point, relative density, affinity for a material, size, shape, weight etc. The larger the difference in the property the easier and the more selective separation will be.

Each of these processes therefore has its specificities and limits and is generally used in relation to the physicochemical properties involved, its selectivity for these properties, the required operating conditions, and the desired degree of separation from partial separation up as far as near-total purification of a product.

Separation processes can be associated with one another, most often in succession, and/or can be repeated under different operating conditions to obtain the desired separation or separations. This chiefly applies to the treatment of complex mixtures and/or those having constituents whose difference in physicochemical properties is small or insufficient necessitating the use of several separating processes involving several different physicochemical properties. This may also be necessary in purification methods intended to obtain a very high degree of purity of a product.

For non-miscible products, of emulsions in particular, several processes can be used, It is first possible to envisage settling of the product before starting to separate the phases.

However for an emulsion and in relation to its stability and droplet size in particular, the time needed for settling may soon become too lengthy.

In addition, if an emulsion does not coalesce it will only be possible to recover part of the continuous phase and a non-negligible part thereof will not be able to be separated. Reciprocally, recovery of the dispersed phase alone will not easily be possible. Coalescence of the emulsion must therefore be induced if it does not coalesce naturally and if coalescence time is too long.

Even after coalescence of the emulsion and recovery of the separate phases, there always remains an interface at which precise phase separation is difficult to obtain, and there often remains a residual quantity of one phase in the other. The interface region must often be removed or re-treated.

It will also be noted that settling methods do not allow depletion of the product contained in a phase in dissolved form if the products are not fully immiscible. It is therefore generally extremely difficult to obtain high purity using a settling method alone and in particular to reach below the saturation threshold of the compound to be depleted in the phase to be maintained.

Another possible solution is to have recourse to distillation of the emulsion.

This solution is not suitable however for all products. First this is a relatively complex operation to implement requiring heavy equipment. Secondly it is generally conducted at high temperature which is most energy consuming and in the worst case may lead to degradation of one or more products of the mixture in emulsion.

It is also to be noted that in the particular case of removing water contained in a crude oil product, this water has a very high salt content, When the water is heated and evaporated these salts tend to deposit in the distillation column leading to corrosion phenomena.

Finally distillation requires a difference in boiling point between the products to be separated and the smaller the temperature difference the more distillation will be difficult and the greater the column height required. To optimise distillation, it is frequently performed under reduced pressure. If the mixture to be separated derives from a pressurized feed line (oil pumping for example) the pressure of the mixture must be reduced. Obtaining a drop in pressure is a costly, complex operation requiring the installation of pressure reducing valves and other systems. Additionally the pressure must frequently be restored for these products so that they can be fed to another installation, Distillation may also be limited in numerous cases by phenomena of azeotrope formation, A third separation technique which can be used is adsorption on solid adsorbent beds such as molecular sieves, silica gels, etc. These types of adsorbents are generally not suitable for mixtures of liquid droplets and heavy hydrocarbons. In addition, the regeneration of these adsorbents requires a high temperature, this being highly energy-consuming.

For non-miscible components, it has also been envisaged to have recourse to a stripping technique.

The stripping technique is a separating process in which a liquid flow is contacted with a gas flow to cause selective transfer of matter between the said liquid flow and gas flow in relation to the relative affinities of the different products between the two gas and liquid phases, the affinity of one constituent for the gas or liquid phase essentially being based on its volatility under the operating conditions and on thermodynamic equilibrium conditions of the constituents in the vapour and liquid phases.

Stripping processes are separation processes of high interest on account of their relative simplicity and since they can be performed under relatively simple conditions arid are low in energy demand.

Therefore one constituent can be depleted from the liquid phase to enrich the gas phase with which it has greater affinity (stripped constituent of the liquid phase stripped by a stripping gas phase towards this gas phase).

It is to be pointed out that the reverse operation consisting of depleting a constituent of the gas phase to enrich the liquid phase with which it has greater affinity (constituent of gas phase stripped by a stripping liquid phase and towards this liquid phase) is generally considered to be a physical or chemical absorption operation and not a gas stripping operation in the strictest sense.

It is therefore to be specified herein that the expression gas stripping>> is to be constmed in the present invention as meaning solely this first variant, namely stripping of the liquid phase by the gas phase. The expression gas stripping is to be understood as strictly designating stripping by a gas, i.e. the gas is the stripping means used allowing the stripping of the constituent to be removed from the liquid phase.

For example the stripping technique is frequently used for the depleting of VOC-type pollutants (volatile organic compounds) and gases dissolved in a flow of water in order to treat this water. In this type of process the transfer takes place from the liquid phase and the VOCs are carried away by the gas phase. It is therefore indeed a gas stripping process in the meaning of the present invention.

As a counter-example, natural gas dehydrating units are known which are operated by stripping with triethyleneglycol (TEG). In these units, the water contained in the gas phase is transferred to the liquid phase (TEG), As explained in the foregoing, this process is not a gas stripping process in the meaning of the present invention since the gas phase is the phase from which a constituent is removed and transferred to the liquid phase. This process is in a fact a process whereby the gas is washed by physical absorption of the water by glycol, The principle of a gas stripping process is therefore to promote the transfer of the constituent to be depleted from the liquid phase towards the gas phase. To do so, the constituent to be removed must diffuse in the continuous phase towards a liquid/gas interface through which it passes and where it volatilises, More specifically, the transfer of matter takes place via a phenomenon of diffusion and desorption of the volatile compound at this interface and being caused by the gas flow. It is based on the thermodynamic equilibrium to be reached by the volatile compound between the two phases.

On account of its higher relative volatility, the compound to be removed has a greater natural tendency to be present in a gas phase until it reaches its saturating S vapour pressure under the temperature conditions applied. Since the gas flow ensures permanent renewal of the gas phase, this saturating vapour pressure cannot be reached by the volatile compound which therefore continuously desorbs from the liquid phase causing its gradual removal from the liquid phase. The desorbing and gradual removal of the volatile compound is governed by the diffusion of the said volatile compound within the liquid phase.

It is to be noted that the volatilisation of the constituent must not be confused with boiling thereof in which case there would be no crossing of a liquid/gas interface and there would be no desorption phenomenon of the constituent. This would be substantially equivalent to distillation.

Therefore, gas stripping techniques chiefly concern the removal of dissolved constituents and are performed under conditions promoting both the diffusion of the said constituent towards the liquid/gas interface and the volatilisation of this constituent at this interface. In general gas stripping processes are therefore aided by relatively high temperatures (remaining lower than boiling point however) and reduced pressure.

The disadvantages mentioned for distillation i.e. energy consumption to heat the mixture and pressure reduction in the network feeding the process, therefore also apply to gas stripping although to a lesser extent.

Several documents can be cited concerning the separation of constituents that are potentially non-miscible with one another.

Document US 5 256 258 concerns the removal of water and other volatile compounds likely to be contained in a heat transfer fluid, For this purpose, the heat transfer fluid is subjected to a stream of nitrogen circulating in counter-current flow which carries away the volatile compounds. It is to be noted that the heat transfer fluid is at a temperature of between 150°C and 400°C. As a result the water and the compounds to be depleted are not present in the fluid in liquid form forming a separate phase, but already in dissolved gaseous form, This document therefore describes a gas stripping process after boiling and entry into dissolved phase of the components to be stripped, Document US 5259931 concerns the purification of water containing dissolved hydrocarbons via air stripping. This document refers to the preamble of document US 4 764 272 mentioning the possibility of treating hydrocarbons not only dissolved in but mixed with water i.e. in emulsion-in-water form. It is to be noted however that US 4 764 272 specifies that the water first undergoes a settling step and that only the recovered aqueous phase i.e. solely containing dissolved hydrocarbons, is subjected to stripping.

The term stripping may even sometimes be ill-used.

For example document WO 20t t/059843 concerns the dehydrating of an oil phase by aspiration generating a flow of stripping air, To achieve this however the oil phase is heated to a temperature higher than the boiling point of water. It follows that the water is no longer in liquid form in the oil phase and no longer forms an emulsion, This process does not correspond either to a stripping process such as previously defined and relates more to distillation under controlled atmosphere and reduced pressure and has the same disadvantages.

There is therefore a major need for a separation process which can be applied to an emulsion and does not have the aforementioned drawbacks or only to a limited extent, Document EP 1 586 620 describes a process for purifying cmde oil comprising a washing step of an emulsified liquid fraction before a stripping step of said liquid fraction whereby a gas is injected in counter-current flow. It is to be noted however that this gas is chiefly used to acidif' the emulsion, The process therefore concerns the transfer of matter from the gas phase towards the liquid phase, which does not amount to gas stripping in the meaning of the present invention, It is also to be noted that it is necessary to have recourse to a final settling vessel to separate the phases of the emulsion.

Document US 5 240 617 also specifically concerns the separation of the phases of an emulsion, and more particularly a water and oil emulsion, by injecting air bubbles into the emulsion, the operation being conducted at a temperature lower than the boiling point of water, It is to be noted that the description in this document lacks details and does not clearly identify which phase of the emulsion is stripped by the air bubbles, It is specified that the air bubbles are injected in finely dispersed manner and that the resulting agitation simply allows thermal homogenisation. The presence of an agitator in the heating circuit of the emulsion targets the same temperature homogenisation.

It therefore appears that the gas in a process according to US 5 240 617 is not capable of stripping constituents of the dispersed phase, the removed constituents in fact belonging to the continuous liquid phase, If the stripped element is water, it is to be understood that the described process therefore mainly applies to an emulsion of oil-in-water type.

The continuous phase by nature being much larger in terms of volume, its removal requires a much longer time if it is desired to recover a maximum amount of the continuous phase or to recover the dispersed phase.

The present invention sets out to overcome the aforementioned disadvantages and for this purpose concerns a process for removing a dispersed phase of an emulsion, characterized in that it comprises a step to subject the said emulsion to gas stripping performed under conditions of temperature and pressure lower than the boiling conditions of the liquid in the dispersed phase,and wherein the composition of said gas is chosen so that the dispersed phase has volatility and affinity with this gas greater than that of the continuous phase of said emulsion.

In the particular case of an emulsion in which it is desired to deplete the dispersed phase, the gas/liquid interface naturally lies between the gas phase and the continuous phase of the emulsion and not between the gas phase and the liquid phase to be stripped. In addition, the dispersed phase by definition is not dissolved in the continuous phase and is not subjected to difftision towards the interface where it can be volatilised. As a result stripping by definition is difficult to apply to an emulsion.

It was therefore surprisingly found that the stripping technique could be applied directly to an emulsion to deplete its dispersed phase without previously having to vaporise the latter in particular by boiling.

Without wishing to be bound by any theory, the injected gas mechanically allows the overcoming of the impossible diffusion through the continuous phase. It is therefore notably possible to cause direct contact between the droplets of a volatile compound and the gas.

In addition, the stripping technique also allows the removal of the constituent of the dispersed phase existing in dissolved form in the continuous phase. With the process it is therefore possible to obtain extremely high purity of the continuous phase, and in particular with a residual concentration of dispersed phase constituent that is much lower than the saturation level of the continuous phase by the said constituent. For application to dehydration of a hydrocarbon phase, it is thus possible to reach a residual concentration of water as low as I ppm.

Advantageously, the gas stripping process is perfbrmed in the presence of means for contacting the gas phase with the dispersed liquid phase. Said means allow the contact surface to be increased between the gas phase and the dispersed liquid phase.

Further preferably, the stripping process is performed in the presence of emulsion break-up means, Breaking-up of the emulsion first promotes contact with the gas phase but also promotes the passing of the constituent or constituents of the dispersed liquid phase into dissolved form in the continuous liquid phase. In dissolved form the constituent(s) are then subjected to the usual stripping process.

According to one variant of embodiment, the contacting means and/or emulsion break-up means comprise means for turbulent gas flow.

Advantageously the gas stripping process is performed with a flow of emulsion, The process can then be a continuous process.

Further advantageously the flow of the emulsion during the stripping step is at least partly turbulent.

Preferably, the emulsion and the stripping gas are in counter-current flow.

Alternatively, the emulsion and the stripping gas may be in co-current flow.

Alternatively or in addition, during stripping the emulsion is injected through spray means, Preferably, during stripping the emulsion passes through at least one packing.

Said packing contributes towards increasing the contact surfaces between the different phases by generating local flow turbulence. In addition it may contribute towards break-up of the emulsion.

Further preferably the packing is a structured lining. Said packings can allow a particularly large specific surface area to be obtained.

Advantageously, the packing is a wire/fibre or thin film packing. Wire/fibre or thin film packings allow better break-up of the emulsion, Further advantageously the thin film packing has a characteristic film thickness of less than 0.25 mm.

Preferably the emulsion passes through several packings, the first packing being the thin film packing.

Advantageously the temperature of the stripping gas is close to, but lower than, the boiling point of the emulsion under the stripping pressure conditions.

By boiling point of the emulsion is evidently meant that it is the lowest boiling point of its constituents.

In addition the temperature of the emulsion is advantageously close to, but lower than, its boiling point under the stripping pressure conditions.

Preferably the stripping step is conducted at ambient temperature, Also preferably the stripping step is conducted under pressure conditions substantially equal to atmospheric pressure.

According to one preferred embodiment the continuous phase of the emulsion is a hydrocarbon phase, In addition thereto the dispersed phase is an aqueous phase, Preferably the aqueous phase comprises methanol or other alcohols, aliphatic alcohols in particular.

The process of the invention may additionally be followed by a condensation step for at least partial condensation of the constituent or constituents of the dispersed phase entrained by the stripping gas.

Further additionally the emulsion is a condensate obtained from a preceding separation step.

According to one advantageous embodiment of the invention the composition of the stripping gas used comprises one or more secondary components present in the continuous phase and differing from the constituent of the dispersed phase to be removed. Said embodiment may be particularly useful if it is desired to increase the selectivity of the process and if the emulsion comprises several volatile compounds likely to be stripped indifferently by the gas phase.

This may notably be the case in an application to remove methanol, even other alcohols (aliphatic in particular such as methanol, ethanol, propanol, butanol and pentanol...) from a light condensate comprising propane or butane for example which it is not particularly desired to remove.

In such case, the stripping gas may be enriched with propane or butane at the time of its injection. The quantity of these compounds present in the stripping gas will limit their extraction from the continuous phase of the emulsion and their entrainment by the gas phase.

Advantageously the secondary compounds are present in the stripping gas used in a proportion close to their gas phase saturation. Therefore the stripping gas already being saturated, it will not be able to entrain more of these compounds.

Further advantageously the process comprises at least one step to recirculate the stripping gas in order to adjust its secondary component composition in the continuous phase.

Said recirculation loop more particularly has two advantages. First it allows the more rapid obtaining of a stripping gas saturated with volatile components after a few cycles without external providing of the constituents under consideration.

Secondly, the recirculation loop advantageously comprises a step to separate the constituents entrained by the gas: the constituents of the discontinuous phase of the emulsion are extracted from the circuit and removed, the constituents of the continuous phase which it is desired to maintain are re-injected into the stripping gas to hold this gas in a state of saturation with these secondary compounds, or are directly recycled in the treated liquid phase. Separation may comprise a slight cooling step to re-condense part of the volatile products.

The present invention will be better understood in the light of the following detailed description with reference to the appended drawing in which: -Figure 1 schematically illustrates the steps of a process according to the invention applied after a three-phase separation; -Figure 2 is a schematic illustration of a pilot unit for implementing a process of the invention, and whose results are given in Figure 3 in graph form; -Figure 4 schematically illustrates one particular embodiment of the a process of the invention; -Figure 5 schematically illustrates one particular embodiment of the invention comprising a recirculation loop and enrichment of the stripping gas with secondary compounds.

Although the present invention is illustrated by a particular application related to the oil sector, it is evidently in no way limited thereto either regarding the field of application or the products used.

When extracting natural gas, the extracted gas may contain condensable hydrocarbons.

Similarly, for petroleum oil undergoing treatment in a refinery, the different processes and treatments applied frequently lead to the formation of a gas phase containing condensable hydrocarbons.

II' this gas has to be transported or handled, the presence of such condensable hydrocarbons should be avoided to prevent the formation of a liquid phase that is undesirable in a treatment or transport method designed for a gaseous effluent. For example, the condensation of these hydrocarbons in a gas pipeline is likely to lead to liquid clogging.

To prevent these problems, the gases containing such condensable hydrocarbons undergo gasoline stripping to adjust the dew point of the hydrocarbons and prevent the condensation of a fraction of the hydrocarbons. This step can be performed in several manners in particular by refrigeration, forcing the condensation of these hydrocarbons.

Since gas is also likely to contain water vapour, there is a risk of hydrate formation. This risk can be prevented by adding a hydrate inhibitor, this inhibitor frequently being methanol (or other alcohols, in particular aliphatic alcohols as mentioned previously).

The hydrocarbons recovered can be given subsequent use in particular in GPL fuels.

Figure 1 schematically illustrates a process of the invention applied to such separation.

For this purpose, the condensate I first undergoes a three-phase separation step (gas 11 -hydrocarbons 12 -water 13) to separate the aqueous phase 13 and the hydrocarbon phase 12. ll

Despite the care given to separation (residence time, etc.) it is extremely difficult to obtain efficient separation of the liquid phases and separation is never perfect.

Therefore the aqueous phase 13 comprises some dissolved and/or dispersed hydrocarbons. The aqueous phase t3 also comprises a non-negligible amount of the added methanol that is partly soluble in the two phases 12, 13.

Similarly, the recovered hydrocarbon phase 12 is not pure. It contains residual dissolved water and dispersed water. Each phase also contains methanol.

So that it can be upgraded this hydrocarbon phase t2 must be purified and in particular dehydrated. Also, for the upgrading thereof it may have to undergo several conversions notably via catalytic processes. Methanol is generally a poison for these catalysts and must therefore be removed before treating these hydrocarbons.

To do so the recovered hydrocarbon phase 12 passes through a pump 14 and is directed towards a column 15 in which it undergoes a first washing step with water which will remove most of the methanol contained in the hydrocarbon phase.

The hydrocarbon phase 12 is injected into a lower part of the column 15 whilst water 16 is injected into the upper part of the column 15.

A central packing t7 ensures the contacting between the hydrocarbon phase 12 and the water 16 to optimise washing and methanol phase transfers.

Although this wash step, like the preceding pumping, mixing and agitation steps, is likely to generate a larger quantity of water dispersed in the hydrocarbon phase 12 leading to the formation of an emulsion, it allows the entrainment of a major part of the methanol and the elimination thereof The methanol-containing water to, is removed at the foot of the column 15, The washed hydrocarbon phase 12' is collected at the head of the column 15 and directed towards a stripping step according to the invention.

For this step, the washed hydrocarbon phase 12' is injected into the top of a stripping column 18.

Preferably, the washed hydrocarbon phase 12' is distributed using a highly efficient liquid distributor compatible with the paclcings used in the stripping column.

Alternatively, the washed hydrocarbon phase 12' is sprayed.

Stripping is performed using a hot, dry gas, e.g. dried air t9 injected at the foot of the column.

Therefore the washed hydrocarbon phase 12' containing an emulsion of water-in-oil type flows down the column 18 whilst the stripping gas 19 rises in the column 8. Circulation therefore occurs in counter-flow.

The washed hydrocarbon phase 12' and the stripping gas 19 both pass through a set of packings 20, 21.

The first packing 20 i.e. the one through which the washed hydrocarbon phase 12' first passes, followed by the stripping gas 19, is more particularly a thin film packing 20 allowing initial breaking up of the emulsion contained in the washed hydrocarbon phase 12'.

Preferably the first packing 20 is a stmctured or wire/fibre packing.

The second packing 21 is also preferably a stmctured packing but it may also be a thin film packing.

When the stripping gas t9 passes through the washed hydrocarbon phase 12', the dispersed methanol-containing aqueous phase has much higher affinity for the stripping gas than the hydrocarbon continuous phase.

Therefore the hot dry gas 19 becomes loaded with water and methanol as it passes in the column 18, The stripping gas is recovered at the head of the column 19 in the fonn of a flow of wet air 22 containing methanol and <<light)) hydrocarbon vapours.

The stripping gas 19 having become enriched with water and methanol, the washed hydrocarbon phase 12' is reciprocally depleted thereof A dehydrated hydrocarbon phase 23 depleted of methanol is recovered at the foot of the column t8.

Evidently, the performance levels can be adjusted as a function of residence time and different flow times, residual water content of the dry stripping gas, packing characteristics.

Figure 2 schematically illustrates a pilot test unit to implement a process of the invention.

This installation comprises a stripping column 200 similar to column 18 intended to allow the counter-flow contacting of a flow of liquid to be purified with a flow of stripping gas.

For example, the column 200 used in the pilot test installation has an inner diameter of 18 inches and is equipped with six structured packing elements having a specific surface area of 250m2 per The liquid is added to the column 200 via an inlet 201 located at the top part of the said column 200, and is evacuated via an outlet 202 at the foot of the column.

The gas is added to the column 200 via an inlet 2t t located in the boftom part of the said column 200 and is evacuated via an outlet 212 located at the top of the column 200, The liquid input into the column 200 is derived from tanks 101, 102 intended to store a quantity of hydrocarbon condensate before and/or after passing through the column 200.

These tanks 101, 102 are mounted in parallel and each one has a filling line 103, 104 and a discharge line 105, 106.

The discharge lines 105, 106 join together at a condensate inj ection pump 107.

Before the condensate is injected into the column 200 via inlet 201, it is first S heated by passing through an exchanger t08 intended to bring its temperature close to that of the gas which will be used for stripping, before being mixed with water injected into the condensate by an injection pump 109 and passing through a mixer.

The turbulent mix (injection of water followed by mixing) of the hydrocarbon condensate and water causes the formation of an emulsion which is injected into the column 200 via the inlet 201.

This emulsion therefore undergoes a stripping step inside the column 200 in counter-current flow by the stripping gas.

The stripping gas used is a flow of nitrogen heated to 50°C and under a pressure of 50 bars.

IS As indicated above, the stripping gas is recovered at the head of the column at the outlet 212 and passes through a depolluting unit 213 called a scrubber before being discharged.

Maintaining of the pressure in the column 200 is ensured by a control valve 214 allowing return of the gas towards the head of the column in the event of insufficient pressure.

After stripping of the emulsified liquid conforming to the process of the invention, the liquid is extracted from the column via the outlet 202 at the foot of the column via an evacuation line 110.

The evacuation line meets up with the filling lines 103, 104 of the tanks tOl, 102 in which the purified condensate can be stored for malysis and for a future test cycle.

Evidently sampling points are provided along the feed and evacuation lines.

In particular, a sample point can be provided before the adding of the emulsion to the column 200 and a sampling point along the evacuation line 110.

Water measurement tests are perfonned on these samples, using the Karl Fisher method in particular.

It is also possible to provide for sampling of the stripping gas at different points of the column 200 to monitor its water uptake, Figure 3 is a graphical illustration of the trend in quantity of water in ppm by weight as a function of time (sampling time).

At each sampling hour the top black dot represents the quantity of water-in-oil in ppm by weight in the emulsion injected at the top of the column. The bottom cross-hatched dot represents the quantity of water-in-oil in ppm by weight in the liquid recovered at the outlet of the column. The intermediate hatched dot coresponds to an intermediate sampling point substantially at mid-column height.

It is to be noted that the curve of the top black dots is evidently offset from the curve of the lower cross-hatched dots which substantially corresponds to the through-time in the column and due to priming of the process.

The results evidently depend on operating conditions, Table 1 below gives some results of the various experiments conducted on an oil phase formed of test condensates having the following characteristics: ASTM distillation (boiling range): 183 °C -203 °C; Flash point: 63 °C; density: 776 kg / m3.

_________ ____________ __________ ___________ __________ ________________

Pressure Temperature Test Input water Stripping Output water condensates content nitrogen content bar kg/h Kgh ppm kg/h ppm by ppm by ___________ _______________ _____________ by voi9 ____________ weighi volume 51 930 2,5 (2000) 2600 ______ _______ 51,8 1900 2,5 (1000) 4000 t _______ 52 2280 3,0 (1000) 4100 <1 <1 50 2300 2,9(1000) 2500 1,2 0.9 40 2310 3,0(1000) 1110 1,6 1.2 60 2310 3.0(1000) 825 1.5 1.1

Table

It is ascertained in particular that to obtain less than I ppm by volume of residual water in the condensate leaving the column, it is useful to increase the flow rate of the stripping gas and/or the temperature.

Table 2 below gives some results of simulations whose model was based on methanol-water-hydrocarbon equilibrium measurements recorded in a methanol removal application such as previously described, the hydrocarbon phase being formed of test condensates such as previously described.

_____ ______ ________ ___________ ______ ______________ _________________

2 Input methanol Output methanol content content C) Ct 0 C) Ht --E. (aqueous (bottom of 0 0 H C) phase) column) Kg/h (ppm ppm ppm bar °C kgh kg/**h kg/h kgb ______ _______ __________ by vol) ________ by wi. by 11!!.

tO 40 23t0 3.0(1000) 1110 0.04 19,4 0,0001 0,04 40 2310 3.0 (1000) 1110 0.45 193.9 0.0085 0.37 40 2310 3.0 (1000) 1110 2.88 1245.2 0.0058 2.50 40 2310 3.0 (1000) 1110 2.88 1245 0.0058 2.50 40 2310 3.0(1000) 1110 2.88 1245 0,0008 0.37 40 2310 3.00000) 1110 2.88 1245 0.0003 0.15

Table 2

Figure 4 schematically illustrates a particular embodiment of a process according to the invention wherein the flow of stripping gas and the flow of liquid to be treated are inj ected in co-current flow.

Said installation comprises a stripping column 300 forming a mixer and comprising at the foot of the column an inlet feed 301 of liquid to be treated and an inlet feed 302 of stripping gas.

All the fluids are evacuated at the head of the column via an outlet 303.

The outgoing fluids 303 are injected into a gas/liquid separator 304 having a liquid outlet 305 at the foot of the separator and a gas outlet 306 at the head of the separator.

The use of this co-current flow system allows an extremely compact installation to be obtained able to be directly installed on a floating or land system when available space is insufficient. The mixer/separator assembly forms a purification stage. Evidently it is possible to provide for several purification stages in series, the liquid flow leaving the separator from a first stage feeding the mixer of a second stage.

Table 3 below gives some results of simulations whose model was based on methanol-water-hydrocarbon equilibrium measurements such as described previously, using a process of the invention operating in co-current flow, The hydrocarbon phase is formed of test condensates having the previously indicated characteristics.

2 Input methanol Output methanol 2. ..

content content rJ 0 0 p C 0 H - _. . (aqueous (bottom of 0 0 H 0 phase) column) / Kg/hpprn ppm ppm bar C kg'h kgb kg/**h ______ ________ ________ by vof) _________ ________ by iv 1. b iv t 40 2310 3.0(1000) 1110 2.88 1245 20.40 2stages 40 2310 3.0(1000) 1110 2.88 1245 5.70 2stages 40 2310 3.0 (1000) 1110 2.88 1245 86.80 1 stage 40 2310 3.0 (1000) 2220 2,88 1245 44.28 1 stage 40 2310 3.0(1000) 2000 2.88 1245 1.80 2stages

Table 3

Figure 5 illustrates the implementing of a process according to the invention comprising a recirculation loop intended to prevent the removal of volatile compounds contained in the continuous phase and whose removal is not desired.

The emulsion to be purified is contained in a tank 400. It may be a water/light hydrocarbon emulsion for example such as presented previously and containing methanol which it is desired to remove.

This emulsion circulates through an exchanger 401 to bring it up to the desired temperature for implementing the process before it is injected into a column 500 via a spray head 501 at the top of this column 500.

The column 500 is fitted with packing 502 similar to the previously described packings.

The emulsion passes through the column 500 and the liquid is recovered at the foot of the column at an extraction point 503.

The stripping gas is used in a closed circuit and recycled through a loop a

description of which will be given.

Conforming to the invention, the stripping gas is injected into the column 500.

The gas is injected into the foot of the column after being circulated through an exchanger 410 to bring it to the desired temperature.

The stripping gas circulates through the column 500 and leaves at the head of the column via an orifice 505.

As indicated for a condensate of light hydrocarbons, the stripping gas will not only entrain the methanol but also part of these light hydrocarbons that are the most volatile under the operating conditions under consideration.

They must therefore be separated from the flow of stripping gas recovered at the outlet of the column 500.

To do so, the gas passes through a cooler 411 before the injection of washing water 412. These subsequently pass through a mixer 413.

The cooling of the gas allows re-condensation of the volatile light hydrocarbons, without re-condensing the methanol. With the washing the methanol is re-dissolved and replaced in aqueous liquid phase. Part of the methanol remains dissolved in the hydrocarbon phase.

The recovered fluid then passes through a three-phase separator 414.

The wet gas phase passes through a dehydration unit 415, e.g. using triethyleneglycol stripping and/or molecular sieve and it is then recompressed 416 and re-injected into the stripping column 500. A supply of gas 417 can compensate for any losses.

The light hydrocarbon phase is recycled and re-injected into the column for a new purification cycle.

The aqueous phase containing most of the extracted methanol is directed towards a treatment unit 418 to treat this effluent.

Another option which can be contemplated is to use the stripping gas which leaves the head of the stripping column as fuel gas (when possible). This option allows simplification of post-stripping treatments which are illustrated in the schematic in Figure 5, Although the invention has been described with a particular example of embodiment, it is evidently in no way limited thereto and encompasses all technical equivalents of the described means and the combinations thereof provided they come within the scope of the invention.