GB2093443A

GB2093443A - A Method and A Device for Purifying a Liquid

Info

Publication number: GB2093443A
Application number: GB8203991A
Authority: GB
Original assignee: Pielkenrood Vinitex BV
Current assignee: Pielkenrood Vinitex BV
Priority date: 1981-02-25
Filing date: 1982-02-11
Publication date: 1982-09-02
Also published as: NL8100927A; NO820579L; MY8500907A; GB2093443B; SG70584G; DE3206000A1

Abstract

A method for purifying a liquid in a cycle, in particular a liquid originating from a mineral oil well, in which the liquid is stripped of suspended components in a closed cycle, and spaces above the liquid are being kept filled with an oxygen-free gas under some overpressure so as to prevent oxygen dissolving in said liquid.

Description

SPECIFICATION A Method and a Device for Purifying a Liquid For expelling, from subterranean rock layers, mineral oil present therein, boreholes are drilled into the layer in question, some holes being production holes, and other ones being used for pressing steam or hot water under pressure into said layer, in order to displace oil from the rock towards a production hole through which, then, a mixture of water and oil, sometimes mixed with solid soil rests, flows upwards. The oil can be separated therefrom, and thereafter the water can be returned towards an injection hole after supplementing possible heat losses by means of additional heating. In this manner the heat supply can be reduced to a minimum.

The recirculated water, however, often contains rests of oil and solids and, moreover, oxygen, which has as a consequence that in the long run obstruction will take place, in particular because of the growths of micro-organisms, deposition of lime and the like. The yield will gradually be reduced thereby, so that the hole is to be cleaned, e.g. by means of an acid treatment.

This is not only an expensive matter as such, but, moreover, leads to a substantial interruption of the operation and, thus, to production losses.

Until now no suitable solution has been found therefor.

The invention provides, now, a method for avoiding these difficulties, which is based on the insight that the recirculation of water should take place without oxygen. The solution provided by the invention is, for the rest, not restricted to the field of application mentioned above, but can be used everywhere where comparable conditions are met with.

The invention provides a method for purifying a liquid in a cycle, which is characterised in that, in a closed separator, the liquid is stripped of components suspended therein, the space above the liquid being kept filled with an oxygen-free gas, preferably at some overpressure, so as to avoid the penetration of air under all circumstances.

In particular the separation takes place, at least for a substantial part, by flotation by means of very small gas bubbles, and as the flotation gas the same gas is used as is present above the liquid in the separator.

Since, in this manner, the liquid is prevented from contacting air, the liquid can be recirculated into the ground without any objection.

In particular natural gas which is often present in situ under pressure can be used as the flotation and protection gas.

For obtaining the desired gas-bubble flotation, a liquid is to be saturated under pressure with a gas, and, after depressurising this liquid, very small gas bubbles will be generated therein. As said liquid particularly the purified liquid is vaporised under pressure in a mixing vessel in which the gas is present under pressure, which is particularly favourable in the case of natural gas present under pressure, since, then, the use of a mixing pump is avoided, which might give rise to an explosion hazard, and, furthermore, such a pump is unfavourable if corrosive substances such as sulphur compounds are present in the water which might attack the pump.

The liquid purified in this manner is, preferably, subjected to a further degasification treatment before being used.

A device for executing this method comprises a separator with a hermetically closed housing which is, above the normal liquid level, provided with a closed gas space, the latter being designed for maintaining therein a substantially constant quantity of gas, which gas space, in particular, is connected to a gas supply and/or discharge by means of a pressure regulating valve.

Preferably this separator is designed for gasbubble flotation, means being present for dissolving the gas which is supplied to the gas space of the separator up to saturation under pressure in the liquid to be supplied to the separator. Said means comprise, in particular, a mixing vessel provided with a vaporiser by means of which the liquid, and in particular a part of the liquid purified in the separator, can be vaporised under pressure, said vessel being, furthermore, provided with a connection for supplying the gas under pressure and for discharging the liquid thus saturated with gas.

The invention will be elucidated below in more detail by reference to a schematic representation of a device according to the invention.

The liquid to be treated is supplied through a duct 1, pumps not shown being included in said duct, which leads to a separator. This liquid is, for instance, hot water originating from a mineral oil production well, in which oil, which has been displaced by steam introduced into the soil in another point, is collected mixed with water.

The separator comprises a normal container 2 in which an inclined plate assembly 3, in particular with corrugated plates, is arranged.

Such plate assemblies are known for separation purposes in various forms so that a more detailed description thereof is not necessary.

The separator shown is designed for separation by flotation. By means of two partitions 4 and 5 a flotation chamber is defined above the plate assembly 3, the latter partition being constructed as an overflow weir via which a floating layer 7 of flotated components floating on the liquid in the chamber 6 can flow off towards a discharge space 8, and, if required, scrapers or the like can be used. The space 8 communicates with a discharge duct 10 provided with a valve 9.

The supply duct 1 opens at 11 in the pointed part 12 of the flotation chamber 6 defined by the partition 4 and the upper wall of the assembly 3.

The water supplied at 1 1 is, then, forced to flow through the interspaces between the plates of the assembly 3, and arrives, thereafter, in a discharge chamber 13, and sediment possibly separated in the assembly 3 can accumulate therein, and can be removed by means of a discharge duct 15 provided with a valve 14.

At the upper end of the discharge chamber 13 a single or multiple overflow weir 16 is present, e.g., as shown, in the form of one or more tubes with a round overflow edge, which weir is, as usual, adjustable in order to allow the liquid level in the container 2 to be adjusted as needed. A discharge space 17 joins the overflow weir 16, and is connected to a discharge duct 1 8 for the treated liquid.

Moreover a duct 20 provided with a valve 19 opens into the duct 1 near the container 2, by means of which a liquid saturated with a gas under overpressure can be injected into the liquid to be treated, the pressure being reduced in the valve 19 to the pressure in the duct 1, so that a great number of very small gas bubbles is generated in the liquid, which arrive, together with said liquid, at 11 in the space 12. These bubbles can adhere to particles suspended in the liquid so that the latter become better flotatable, and also particles heavier than the liquid can be made flotatable. In this manner the separation effect can be considerably improved.

The particles flotating in the space 12 are collected in the floating layer 7, and in the assembly 3 an after-separation of flotatable components and, as the case may be, entrained gas bubbles can take place. As already mentioned, heavier components separated in the assembly 3 will collect on the bottom of the chamber 13. Thus far the operation of the device according to the invention is the same as of a similar known separator.

However the present device distinguishes itself from the known ones in that the container 2 is hermetically closed at its upper side by means of a cover 21, which cover also covers the spaces 8 and 17. In the cover 21 a gas duct 23 provided with a pressure regulating valve 22 opens, originating from a source of gas under pressure not shown, said cover, furthermore, being provided with a security valve 24 connecting to a gas discharge duct 25 through which the gas removed through the valve 24 can be discharged, if required for being supplied to the duct 23 under a suitable pressure. The valves 22 and 24 are adjustable so that a suitable pressure is -maintained in the space 26 between the cover 21 and the liquid in the container.

The gas supplied through the duct 23 is the same gas as the gas introduced at 19 in dissolved condition into the duct 1. The water discharged at 18 can be reintroduced into the soil, if necessary after being additionally heated. This cycle can be completely closed, so that nowhere oxygen from the air can enter anymore. Under such circumstances the oil containing earth layers and the supply pipe will no longer get obstructed, in particular if the water has been effectively stripped of oil rests and solid components. This, now, is ensured by the used gas-bubble flotation, and the gas overpressure ensures that no oxygen can penetrate into the cycle.

As the gas any oxygen-free gas can be used. In practice one will, generally, use nitrogen or natural gas, in particular when the latter is present under pressure in situ.

The water discharged at 18 comprises, of course, some gas dissolved therein under some pressure. This gas is removed in a degassing vessel 27, after which the degassed water can be discharged by means of a pump 28 and a duct 29.

The gas is removed via a duct 30 which, in particular, can connect to the duct 25. This degassing vessel 27 can, for the rest, be left out if in the space 17 sufficient degassing occurs already, and this space can, if required, be separated from the space 26 to that end.

The duct 20 can be connected in the usual manner to a compression pump which is adapted to supply pure water and gas mixed at the desired pressure. If, however, the gas in the duct 23 is under a high pressure, as for instance in the case of natural gas, mixing with water can lead to difficulties. Moreover mixing the gas in a pump can be undesirable because of a possible explosion hazard and/or corrosion.

Under all circumstances, however, an effective mixing of gas and liquid under pressure can be obtained by using a mixing vessel schematically indicated at 31, in which, at 32, pure water withdrawn from the space 13 is supplied by means of a pump 23 and a one-way valve 34, the water supplied being vaporised at 35 into the upper part of the vessel 31. Into the vessel gas from the duct 23, if required after pressure reduction in a throttle valve 36, is introduced, which gas, then, can dissolve in the vaporised water. The water saturated under pressure with the gas is, then, discharged again via the duct 20.

The supply of gas and water into the vessel 31 can be controlled in any suitable manner, for instance in correspondence with the quantity of water in the vessel and the gas pressure prevailing therein.

The quantity of liquid injected at 19 is smaller than the quantity supplied by the duct 1. If the quantity of gas dissolved in the water discharged at 18 is larger than the quantity of gas introduced at 19, the quantity of gas in the space 7 will diminish, which will, then, be supplemented by the valve 22, and under opposite circumstances a gas excess will be removed by the valve 24.

The removal of flotatable material and sediment occurs by intermittently opening the valves 10 and 14 respectively, which takes place below the liquid surface, and, because of the overpressure, no air can penetrate.

It will be clear that within the scope of the invention many modifications are possible. For instance the gas introduction for gas-bubble flotation can also take place directly into the space 12.

Claims

1. A method for purifying a liquid in a cycle, characterised in that the liquid is stripped of the components suspended therein in a closed cycle, the space above the liquid being kept filled with an oxygen-free gas under some overpressure.

2. The method of claim 1, characterised in that the separation takes place by flotation by means of very small gas bubbles, and, as the flotation gas, the same gas is used as which is present above the liquid.

3. The method of claim 1 or 2, characterised in that the gas is natural gas under pressure.

4. The method of any one of claims 1-3, characterised in that the purified liquid is vaporised under pressure in a mixing vessel into which the gas is introduced under pressure.

5. The method of any one of claims 1-4, characterised in that the purified liquid is led through a degassing vessel.

6. A device for executing the method of any one of claims 1-5, characterised by a separator with a hermetically sealed enclosure, comprising a gas space above the normal liquid level, adapted for maintaining therein a substantially constant amount of gas.

7. The device of claim 6, characterised in that the gas space of the separator is connected to a gas supply and/or gas discharge by means of a pressure regulating valve.

8. The device of claim 6 or 7, characterised in that the separator is designed for supplying thereto a liquid saturated under pressure with a gas after decompression thereof.

9. The device of claim 8, characterised in that the mixing of the gas and the liquid occurs in a mixing vessel provided with a liquid vaporiser connected to a liquid compression pump, and with a supply of gas under pressure.

10. A method and device substantially as hereinbefore described with reference to the accompanying drawings.