WO2024013510A1

WO2024013510A1 - Gas flotation apparatus & method

Info

Publication number: WO2024013510A1
Application number: PCT/GB2023/051849
Authority: WO
Inventors: Paul Randal Neil MCALISTER; Franciscus Johannes WURPEL
Original assignee: Adaptive Process Solutions Ltd
Priority date: 2022-07-13
Filing date: 2023-07-13
Publication date: 2024-01-18
Also published as: GB202210294D0

Abstract

The present invention relates to fluid treatment apparatus and methods, especially treatment of contaminated water, and more particularly to improved gas flotation apparatus and methods. The present invention relates to the use of both Dissolved Gas Flotation and Induced Gas Flotation in produced water plants without having to rely on any additional external separator vessels. A method of separating contaminants from a fluid is disclosed, the method comprising the steps of (1) Taking a feed fluid of water with lower contamination levels from a downstream point of a produced water plant; (2) Infusing the feed fluid with gas thereby creating microbubbles; and (3) Injecting the microbubble infused feed fluid from stage (2) into one or more upstream points with higher contamination levels in the produced water plant. Furthermore, apparatus for carrying out the method and testing methodology and apparatus are also disclosed.

Description

GAS FLOTATION APPARATUS & METHOD

Description

Field of the Invention

The present invention relates to fluid treatment apparatus and methods, especially treatment of contaminated water, and more particularly to improved gas flotation apparatus and methods.

The present invention relates to a novel improvement in the process of treating water (or other fluids) with gases to generate microbubbles for the purpose of oil, fat and solids removal.

The present invention can also be used to improve the process of infusing water or other fluids with microbubbles or dissolving gases in water or other fluids, where they can be used to alter the physical and chemical properties of the water or other fluid for the purpose of contaminant dissolution, dispersion or removal.

Background to the Invention

Microbubble Gas flotation process is a long-established art whereby gas bubbles are added to water where they interact with oil and/or grease and/or fat droplets and/or solids helping them to float to the fluid surface, from where they can be removed.

The invention improves the processes of infusing water or other fluids with microbubbles or dissolving gasses into water and other fluids. Dissolved gas can be used to alter the physical and chemical properties of the water or other fluid to effect physical and chemical changes which enable pH change, contaminant dissolution, dispersion or removal and to affect changes such as to improve separation performance, improve contaminant removal, dissolve solids or precipitate contaminants.

Dissolved gas can also be used to promote organisms or kill organisms. The use of microbubbles in the size range of 5-1000 pm mean bubble diameter, is established art.

Micro-bubble infused water may be recirculated within a defined vessel or skid for the purposes of maintaining sufficient overall fluid flow in low production (i.e. fluid input) environments, but not from one point in a water treatment plant to another to specifically increase separation performance.

Dissolved gas refers to gas that is truly dissolved in water and not present in bubble form. “Dissolved Gas Flotation” (or “DGF”) refers to the established art whereby gas is dissolved into a fluid at pressure using a centrifugal pump, turbine pump or other method of dissolving gas into water. The fluid pressure is then lowered causing gas to break out, forming microbubbles typically in the 5-100 pm range.

“Induced Gas Flotation” (or “IGF”) refers to gas bubbles in the larger 100- 1000 pm mean diameter bubble size range. These bubbles are typically generated using a venturi-gas suction device to draw lower pressure gas into the higher-pressure motive fluid stream, generating micro-bubbles in the 100-1000 pm mean diameter bubble size range. Other methods can also be used to generate bubbles in this size range. Summary of the Invention

According to a first aspect of the present invention there is provided a method for separating contaminants from a fluid, the method comprising the steps of:

1) Taking a feed fluid of water with lower contamination levels from a downstream point of a produced water plant;

2) Infusing the feed fluid with gas thereby creating microbubbles; and

3) Injecting the microbubble infused feed fluid from stage (2) into one or more upstream points with higher contamination levels in the produced water plant.

Microbubbles float contaminants from the higher contaminated water point for removal from the produced water plant.

No additional separator vessel is required for this method, nor does there require to be a wholly uncontaminated fluid supply for gas injection. The method recycles the available most decontaminated fluid to assist in further decontamination of the fluid by micro bubble gas separation.

The gas bubble carrier fluid may be water or any available liquid.

The contaminated fluid may be from an oil and gas process or may be from any process where contaminated fluid may require decontamination. This may include temporary/permanent ponds and the like. The method may improve the control of injection fluid gas saturation to maintain optimal gas saturation levels by using a controllable internal recycle stream of water (or other fluid) and infusing it with gas. The water/fluid can be recycled until it is optimal for the gas flotation process or until it is fully saturated (i.e. no further gas can be dissolved into the liquid).

The microbubble gas-flotation process works as follows:

Stage 1. A suspension of micro-bubbles is generated in the water or other fluid body

Stage 2. The microbubbles then collide with contaminant particles or droplets

Stage 3. The microbubbles and contaminants coalesce together to form larger particles or droplets or buoyant agglomerations

Stage 4. The buoyant particles, droplets or agglomerations then float to the surface

Stage 5. The surface layer of the fluids containing the contaminants can then be removed.

Microbubbles in the range of 5-100 pm are most effective for colliding with and coalescing with small oil droplets and solids.

Larger gas bubbles in the range of 200-1000 pm are most effective for colliding with and coalescing with larger oil droplets.

A produced water treatment plant normally comprises water treatment equipment, interlinking pipework and sometimes storage tanks and vessels (such as gravity separators, gas floatation units, hydro-cyclones, dissolved gas flotation units, collection vessels, plate separators, settling tanks, settling ponds, surge tanks, other vessel types, other water treatment devices, etc).

The prior art is to inject gas micro-bubbles into a particular produced water treatment node or vessel where stages 1 -5 take place. There may be some carry through of microbubbles to the next node or vessel, however the bubbles naturally coalesce with each other and become “spent” when the mean bubble size is too large and gas saturation becomes suboptimal for stages 2-5.

The object of this method is to use the whole produced water treatment plant to promote the various stages of the gas flotation process by maintaining optimal gas micro-bubble saturation throughout the plant. Nearly all stages in the water treatment plant can facilitate one or more of the 5 stages listed above. For example, even an interconnecting pipe can facilitate stages 1-4 of the gas flotation process outlined above. A degassing vessel fitted with an oil collection bucket could be used for stages 1-5 of the process. The key to maintaining optimal performance across stages 1-5 gas flotation process is to ensure that the water stream remains saturated with optimal levels of gas microbubbles.

This is achieved in two main ways:

Firstly, the microbubble flotation process apparatus has its own dedicated liquid recycle stream which enables the gas saturation to be varied and controlled to optimal levels or until fully saturated before it leaves the microbubble infusion skid. Secondly, a proportion of the water stream (or other fluid stream), typically 10-50% is removed from a downstream location in the produced water plant where there are lower contamination levels, to be used as the gas carrier fluid. The gas microbubble infused water (or other fluid) stream is then reinjected at an upstream location where the contaminant level is higher. The flowrate of the injection stream can be varied to increase or decrease gas saturation levels in the main water (or other fluid) treatment stream. This process can be repeated where microbubble infused water is injected at several different upstream points in the water treatment plant to ensure optimal conditions for stages 1-5 of the gas flotation across the plant.

According to a second aspect of the present invention there is provided a method of modifying an existing fluid contaminant separation system which includes one or more contaminated fluid inlets, and one or more fluid outlets comprising the steps of:

Step 1 . draining an at least partially decontaminated fluid at a first point between the one or more fluid inlets and one or more fluid outlets;

Step 2. injecting a separating gas into the at least partially decontaminated fluid;

Step 3. injecting the separating gas treated at least partially decontaminated fluid into a second point on the existing fluid contaminant separation system; wherein the first point is upstream of the second point.

Alternatively, waters from other sources of relatively clean water can be sourced (e.g. aquifer water, treated seawater, an adjacent produced water stream) as feed water for the gas microbubble generation skid.

Fourth Aspect - Multiple Gas Bubble sizes and combinations:

The microbubble generation apparatus contains two water streams: Stream 1 Incorporates a device (such as a centrifugal or turbine multiphase pump) to dissolve gas in the water or other fluid (Scenario 1). Gas microbubbles of 5-100 pm s are created when the pressure is released at point of injection, not in the actual apparatus itself (Scenario 1)-

If the gas inlet to this device is closed, no gas bubbles are generated (Scenario 2).

Stream 2 incorporates devices which takes a proportion of Stream 1 as the feed water and generates gas bubbles using a venturi suction device, sucking in lower pressure gas into the higher-pressure water stream.

The same device or a separate device can also be used to inject higher pressure gas into the lower pressure water stream. There is a static gas mixing device installed downstream that can be used to cap mean bubbles size from the aforementioned suction/injection device to less than 300 pm. If the static gas mixing device is not used, then gas bubbles will be in the range of 100-1000 pm. These microbubbles are created in pressurised fluid from Stream 1 which does contain dissolved gas (Scenario 1) or does not contain dissolved gas (Scenario 2).

This means that the following gas bubbles combinations can be injected for optimal separation performance: • DGF only to point or points. DGF microbubbles are fed to a single injection point or group of injection points simultaneously.

• IGF only to point or points. IGF gas microbubbles are fed to a single injection point or group of injection points.

• IGF/DGF/DGF combined to the same point or points. Fluid containing a combination of IGF/DGF gas bubbles can be injected into a single injection point or group of injection points at the same time as fluid containing DGF gas microbubbles only is injected into the same injection point or group of injection points.

• IGF/DGF and DGF fed to separate points or groups of points. Fluid containing DGF/IGF gas bubbles are injected into a single/group of injection points at the same time as water containing DGF gas bubbles only is injected into separate injection point or group of injection points.

If the apparatus is fitted with a second centrifugal or turbine pump then the following additional scenarios are possible:

• IGF/DGF combined to the same point or points

• IGF and DGF fed to separate points or groups of points.

Fifth Aspect - up to 2 gas feeds:

The Micro-bubble generating apparatus can source more than one gas or gas blend simultaneously to achieve optimal gas chemistry to facilitate decontamination of water or fluids. Stream 1 (DGF) and Stream 2 (IGF) can draw gas from two separate locations on a production plant.

Examples:

1 . Fuel gas - e.g. 95% Methane and 5% Carbon Dioxide

2. Second stage separator gas - e.g. 98% Methane 2% Carbon Dioxide

3. Nitrogen from platform Nitrogen generator - e.g. 99.9% Nitrogen

4. Exhaust Gas (often used for Tank blanketing) - e.g. 18% Carbon Dioxide, 88% Nitrogen

The gas can be selected for optimal water treatment performance:

Examples:

• Nitrogen does not dissolve easily in water and tends to favour the IGF process.

• Methane is more soluble in water than Nitrogen and usually more effective for the DGF process.

• Carbon dioxide is highly water soluble and strongly favours the DGF process meaning higher gas saturation. Carbon Dioxide also lowers the pH of the water which often improves the oil water separation process and also aids the removal of various Water Soluble Organic compounds including Naphthenates in particular. WSO species include long Organic Acids (>C7+), Phenols, BTEX (Benzene, Toluene, Ethylbenzene, Xylene), NPD (Nathelene, Phenanthrene, Dibenzothiophene), PAH (Polycyclic Armoatic Hydrocarbons) and Napthenatic Acids and Salts.

Sixth Aspect of the Invention -Assessing Gas Flotation Contaminant Rise Velocity Versus downward velocity in gravity separation nodes or vessels.

This invention uses an existing produced water treatment system comprising of various treatment nodes or vessels. For the gas flotation process to work, downward velocity of the main fluid in a gravity separation node or vessel, must be lower than the rise velocity of contaminants/gas bubble agglomeration (in the gas flotation process). For cost and time reasons, it is preferable to establish in advance of a full scale pilot trial if gas flotation has strong potential for success. For this reason a small scale dynamic flotation test apparatus has been developed to measure the maximum downward velocity that the gas flotation method can tolerate for a given fluid. The test uses fresh or live fluids injected with IGF and DGF micro-bubble combinations. The apparatus flows the main contaminated fluid through a vertical separating vessel in the downward direction, i.e. from top to bottom. A proportion of the fluid (10-50%) is removed from the base of the vessel, infused with gas microbubbles and reinjected to the inlet of the vessel. Contaminants rise to the top of the vessel from where they remain suspended or are skimmed off. Multiple runs are carried out, each with increasing downward fluid velocity, contaminant levels are measured at the inlet and outlet of the vessel to assess removal performance, when removal performance deteriorates significantly, the maximum downward velocity hs been exceeded. The downward velocity for each process node within a client system is calculated and compared against the results of the test-work to indicate potential gas flotation efficacy and support the decision to proceed to full scale field trial.

The configuration described is suited to Brownfield retrofit applications and also some Greenfield applications. For other Greenfield applications and some Brownfield applications, a slightly different system may be used to the same end.

The inlet to the microbubble generation apparatus is set up in the same way as previously. There are two key differences:

Firstly, instead of using multiple conduits from the process skid or its near vicinity, a single main conduit can be installed leading from the outlet of the process skid, which is used to distribute water containing dissolved gas to any point in the upstream produced water plant by way of smaller T-off conduits.

Secondly a re-circulation line may be used to recirculate the water containing dissolved gas or entrained gas bubbles back through the bubble generation apparatus.

The ring main conduit described above helps to maintain stable pressure, reducing any gas breakout in the line.

Gas flotation in the oil and gas industry is historically applied to treat fluids in vessels or nodes of 5-6 bar pressure. This is driven in part by the normal operating limit of multiphase centrifugal pumps used for bubble generation. To enable higher pressures process nodes or vessels to be targeted, a centrifugal can be installed in the feedline to the Microbubble Generation Pump to provide a positive feed pressure. For example, a feed pressure of 10 bar enables a Microbubble Flotation Process Apparatus that can deliver a differential pressure of 6 bar, to inject into a process node or pressure vessel operating at 16 Bar pressure.

Gas stripping of volatile contaminants:

The ability to use the existing plant for multi stage injection of dissolved gas or microbubbles is excellent for improving the stripping other gases or volatile contaminants (e.g. Hydrogen Sulphide, Methane) from fluids or water.

For effective gas stripping the feed gas should have zero or very low concentrations of the target contaminant.

IGF and DGF bubbles can be injected separately or in combination to single or multiple injection points.

The invention enables 2 gases to be used for microbubble generation in separate streams that can be injected separately or combined.

The invention can dissolve Carbon Dioxide from influent gases to reduce pH for WSO removal and improved oil and water separation.

The invention can use a circulating ring main configuration to maintain dissolved gas at pressure, releasing microbubble infused treatment water to multiple nodes or pressure vessels.

The invention can be used for multiphase gas stripping for removal of dissolved or dispersed gases and volatile compounds.

Notes and Definitions

All gas bubble, oil droplet or solid particles sizes stated in pm (microns) refer to mean diameter.

“Dissolved gas” describes truly dissolved gas, although this may be broken out by pressure reduction to form micro-bubbles.

“Gas saturation” refers to the total gas content of water including dissolved gas and micro-bubbles.

All gas bubble, oil droplet or solid particles sizes stated in pm (pms) refer to mean diameter.

The presently described process enables treatment enables treatment of produced water streams with much higher contamination levels than possible using prior art methods.

The prior art is to use gas flotation in defined treatment vessels or nodes as a polishing technology to treat relatively clean waters with relatively low oil in water contamination levels. This is because the main bubble generation methods (such as centrifugal pumps, turbine pumps and venturi suction bubble generators) can cause shear of oil droplets, meaning that larger oil droplets can be sheared into smaller oil droplets.

If there is a high level of oil in water contamination, large quantities of very small oil droplets will be created, causing stable emulsions and poor oil water separation performance.

The process utilises the cleanest feed water available from the downstream end of the plant and this means that oil concentrations are low and residual oil droplet sizes are already low and less likely to shear into even smaller oil droplets.

In summary, the “clean” water recycled from the downstream end of the plant can be used to treat produced water treatment streams with very high levels of oil in water contamination.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

Fig. 1 is a schematic representation of a micro bubble diffusion unit connected to an FPSO storage tank;

Fig. 2 is a further schematic representation of a micro bubble diffusion unit connected to a simple process;

Fig. 3 is a schematic depiction of a first embodiment method according to the first and second aspects of the present invention and an apparatus according to a third aspect of the present invention; Fig. 4 is a schematic depiction of a second embodiment apparatus according to the third aspect of the present invention; and

Fig. 5 is a schematic representation of a testing apparatus according to a fourth aspect of the present invention.

The invention generally relates to removing a portion of fluid (in most cases water) flow from a downstream region or regions of a fluid processing plant (i.e. less contaminated than upstream fluid) and injected with microbubbles using a micro-bubble generating device.

A gas saturator device 10 will mix gas (Hydrocarbon gas, Nitrogen, Carbon Dioxide; Exhaust Gas and other gases or blends) into the removed fluid such that the fluid then contains dissolved gas and/or micro-bubbles.

The gas/fluid mixing device 10 contains a specially designed pump (not shown) for mixing free gas and fluid, thereby generating dissolved gas infused water. The microbubble infused water is then transferred to a pressure-controlled vessel that is contained within a skid (not shown) provided to house the various components.

The water flow that exits the pump contains dissolved gas under pressure, that has not yet been liberated by a pressure drop to form microbubbles.

There is the option to add micro-bubbles immediately downstream within the skid using a device which uses either venturi gas suction or a positive pressure injection to generate bubbles in the range 10-100 pm. A second sheering device may be used to break up bubbles above 300pm, effectively capping maximum mean diameter bubble size to around 300 pm.

In summary, the gas dissolved by the pump remains fully or almost fully dissolved in the fluid. Additional gas bubbles are then added to the fluid using gas suction and/or injection to add gas. The pressure is released at point of injection meaning that there are up to three main bubble size ranges present within the range 5-100 micron, 100-300 micron and 300- 1000 micron.

The skid has a recycling capability which enables the fluid to be recirculated back through the mixing pump enabling control and optimisation of gas saturation. Furthermore, this enables greater flexibility in regards of flowrate through the pump.

Furthermore, the pump motor (not shown) can be fitted with variable speed drive providing further flexibility, control and energy efficiency.

The system is connected to a distribution manifold (not shown) with control valves (not shown) which enables several gas infused water streams to be distributed at varying flowrates to more than one targeted upstream locations in the fluid treatment plant to achieve optimal localised fluid treatment performance and overall fluid treatment performance.

The water containing the microbubbles is injected to an upstream point or points in the water/fluid treatment plant, where it will mix and flow through existing pipework and vessels (such as gravity separators, gas floatation units, hydro-cylones, dissolved air flotation units, collection vessels, plate separators, settling tanks, settling ponds, surge tanks, other vessel types, other water/fluid treatment devices, etc) where oil and/or grease and/or fat droplets and/or fine solids will coalesce with gas bubbles and/or float to the surface and/or be skimmed off.

This technology can be used to treat water associated with storage tanks. Water 11 can be removed from the tank 12, then infused with micro-bubbles 13 and transferred to the same tank 12 or another tank (not shown) to enable gas and oil and/or grease and/or fat droplets and/or fine solids 14 to coalesce and float to the surface. Oil and/or grease and/or fat droplets and/or fine solids 14 can be removed from the surface and/or clean water 16 can also be removed from the tank bottom. See Fig 1 .

On oilfield installations with availability of exhaust gas, exhaust gas 17 (carbon dioxide, water vapour and nitrogen) can be used for the purpose of microbubble generation and flotation and may also be dissolved in waste water for the purposes of pH control (formation of carbonic acid). Alternatively liquid or gaseous carbon dioxide 18 can be used for the purpose of microbubble generation.

Alternatively, some oilfield installations naturally produce high quantities of carbon dioxide which is lost from the separation system as pressure drops from high to low though the various stages of oil, gas and water separation. Gas can be sourced from the upstage process, or from the fuel gas system and injected by way of micro-bubbles into the downstream lower pressure process, replacing lost Carbon Dioxide and lowering pH. Such gas may be carbon dioxide, but may also be gas quads, fuel gas, exhaust gas, FPSO blanketing gas, etc.

Water Soluble Organics or WSOs vary in toxicity, may bioaccumulate in the aquatic environment and are of increasing concern, improved practice and regulations have been introduced in countries such as Norway and Brazil.

Problematic WSO species include long Organic Acids (>C7+), Phenols, BTEX (Benzene, Toluene, Ethylbenzene, Xylene), NPD (Nathelene, Phenanthrene, Dibenzothiophene), PAH (Polycyclic Armoatic Hydrocarbons) and Napthenatic Acids and Salts (previously discussed).

The above WSO species demonstrate different properties from the perspective of gas treatment, falling into four main categories:

1 . Those which are truly soluble in produced water under the produced water system limitations and cannot be removed by treatment with gas and or microbubbles.

2. Those which are predominantly oil soluble. These WSOs are entrained in normal hydrocarbon oil droplets, greater quantities can be removed due to the improved efficiency of the presently described gas flotation process.

3. Those which can be removed by gas stripping to remove more volatile WSOs. The presently described process use the existing water treatment plant for multiple stage gas flotation (multiple vessels and nodes) and can use the multiple gas removal conduits to remove volatile WSOs along with the gas phase.

4. WSOs that can be partitioned from the water phase into the oil phase for removal by way of pH reduction. The flexibility of the presently described gas feed line(s) and the capability to control gas saturation by adjusting the recycle rate in the water treatment plant and within the process skid itself, enables control of carbon dioxide concentration for targeted pH reduction and optimal removal of WSO contaminants.

The gas saturation and thereby the pH of the water can be controlled using the recycle on the apparatus 10 to maximise concentration and acidify the fluids with Carbonic Acid. Potential applications of pH adjustment include pH adjustment for optimal oil in water separation, scale prevention and Napthenate control. Fig. 2 shows such an arrangement. Water 19 is drawn downstream of a process 20 (shown as a simple pipe in Fig. 2) and passed through the diffusor 10 to infuse with micro-bubbles which may be sourced either from exhaust gas 17, a separate liquid/gaseous carbon dioxide source 18 or a combination of the two. The micro-bubble infused water 21 is then reinjected upstream of the draw point. The water 21 has a lower pH because of the addition of carbon dioxide. Flow direction is indicated by the arrow on Fig. 2 and is from right to left from the perspective of Fig. 2.

As described above water can be recycled within the locale of the pump module 10 and from points on the water treatment plant enabling gas saturation to be varies and controlled. For gases that are chemically active in solution, such as oxygen and carbon dioxide, this means that gas concentration can be accurately controlled for numerous beneficial purposes such as gas flotation, gas scrubbing, pH control, microbial control, scavenging of impurities.

An apparatus and method for separating one or more contaminants from a fluid stream is depicted in Fig. 3 and generally referred to as 110. In the present embodiment, the fluid is produced water and is obtained from an oil and gas production facility, such as a production platform (not shown) but it will be understood that the present apparatus and method may be used for any suitable contaminated fluid source, particularly those where the fluid is mainly water.

Comingled production fluids from the production wells 112 are fed via a production manifold into an initial, primary or high pressure (“HP”) separator vessel 114. This functions much as any prior art well fluid separator vessel.

A production fluid conduit 116 is connected between the HP separator 114 and a secondary, medium pressure or “MP” separator 118. The MP separator 118 is again one typical of the art and works much in the same fashion as the HP separator 114. The primary well fluid conduit 116 transports production fluids from the HP separator 114 to the MP separator 118.

A secondary well fluid conduit 120 is connected between the MP separator 114 and a tertiary, low pressure or “LP” separator 122. The LP separator 122 is again one typical of the art and works much in the same fashion as the HP separator 114 and MP separator.

A primary, high pressure or “HP” hydro-cyclone 132 is connected to the HP separator 114. A primary water conduit 134 allows decontaminated water pooling within the HP separator 114 to be transferred to the HP hydro-cyclone 132. The HP hydro-cyclone 132 is of a known type and functions to remove further particulates and contaminates from the water pooling in the HP separator 114.

A secondary, medium pressure or “MP” hydro-cyclone 140 is connected to the MP separator 118. A secondary water conduit 142 allows decontaminated water pooling within the MP separator 118 to be transferred to the MP hydro-cyclone 140. The MP hydro-cyclone 140 is of a known type and functions to remove further particulates and contaminates from the water pooling in the MP separator 118.

An HP hydro-cyclone water outlet conduit 158 transports water from the HP hydro-cyclone 132. An HP level control valve 160 is provided on the HP hydro-cyclone water outlet conduit 158 and controls when water is allowed to pass from it to the downstream system water supply conduit 156.

Similarly, an MP hydro-cyclone water outlet conduit 162 transports water from the MP hydro-cyclone 140. An MP level control valve 164 is provided on the MP hydro-cyclone water outlet conduit 162 and controls when water is allowed to pass from it to the downstream system water supply conduit 156.

The downstream water supply conduit 156 feeds firstly into a tilted plate separator 123, and then onto a compact flotation unit 165, and then onto a degasser vessel 166, before going onto a produced water settling tank 167. A water outlet 168 allows water pooling in the degasser vessel to exit the system 110.

The foregoing description represents a typical prior art well fluid Produced Water system common in the field.

In the present embodiment, a gas saturation module 10 is provided on the system. This may be included with the installation of the entire system or may be added to an existing system to augment it. The module may be provided on a skid and hooked and unhooked from the system as necessary or may be permanently installed for permanent augmentation of the system.

The flotation gas module 10 contains a special gas liquid mixing pump which will mix in fuel gas, air or other gases to infuse the water with micro bubbles. A further flowline will transfer the microbubble infused water back from the Module to any upstream injection point. This pump will also provide the motive force to recirculate the water and gas from the downstream source or sources to the upstream injection point or points. An additional pump (not shown) may optionally be added to provide additional motive forces if required.

A flotation gas supply line 196 and a liquid supply conduit 198 supply the gas saturation module 10 with flotation gas and liquid respectively. The water supply conduit 198 branches off from any downstream clean liquid source shown as “A” in the drawing. The additional gas saturation module 10 combines the recycled water with any available flotation gas. The discharge infused water conduit 1100 will transfer the micro bubble infused water to any upstream injection point. Unlike prior art solutions, no additional separator vessel for the flotation gas module is required since it uses any available existing vessel.

A gas saturated water outlet valve (not shown) is provided on the gas saturated water conduit 1100. The valve (not shown) is the pressure control valve of Module 10 and has been deliberately removed from the skid to enhance the control of injecting the microbubbles at the desired injection point shown as “B”. Placing the pressure control valve as close as possible to the injection point will reduce I eliminate undesired premature gas bubble coalescence, and hence improve separation efficiency.

The gas saturated water coming from the module will be in the “microbubble” range of approximately 10-1000 pm, the MiFU has significant control over the bubble sizes within the range, including the traditional IGF and DGF bubble sizes typically 10-100 pm and 100-300 pm respectively, with capability to deliver up to 1000 pm.

The internal and external recycle rates will be variable and adjusted according to process requirements, offering microbubble flotation of oil and solids, optimisation of gas saturation, and optimisation of vessel retention time. The recycle rate will be automatically adjusted by the module control system as produced water production rates increase (or decrease) to maintain optimal flotation performance.

The recirculated micro-bubble infused water will be applied upstream of produced water treatment vessels, such as gravity separators, plate separator vessels, open/closed drains vessels, cyclical vessels, produced water collection vessels, degassers, larger bubble flotation units/compact flotation units, degassing vessels, produced water caissons, closed drain tanks, open drains tanks. The technology will also work in horizontal and vertical vessels.

This process can also be used to create microbubble infused water and to pump this into water streams being removed, transferred from FPSO, FSU, FSO slop, cargo, storage tank or tanks and transferred back into the same tank or another other slop, storage, cargo tank.

The microbubbles will then enhance separation by providing gas flotation to float contaminants to the surface of the receiving tank or vessel.

Micro-bubble infused fluids can also be injected into the fluids being recirculated, recycled, transferred from FPSO, FSU, FPS, slop and/or cargo tank or storage tanks back into the topside production system, produced water for further processing.

This process can be retrofitted to existing produced water treatment vessels for enhanced contamination removal performance in existing vessel or vessels or added vessel or vessels.

In most produced water systems, the temperature trends from high to low from upstream to downstream. The residual oil droplet size trends from large to small.

IGF gas sized bubbles are more effective at high temperature (boiling point being the upper limit) than DGF sized gas bubbles which have an upper temperature limit of around 68C due to decreasing solubility with rising temperature. DGF bubbles are normally more effective at targeting small oil droplets than larger IGF gas bubbles.

The apparatus has the capability to deliver water infused with IGF bubbles to upstream points and DGF gas flotation points simultaneously leading to optimal localised flotation performance.

This process can also be installed in new build production systems, often referred to as greenfield produced water systems to enable gas flotation to be utilised with the same benefits identified above.

The configuration described above is ideal for Brownfield retrofit applications and also some Greenfield applications. For other greenfield applications and some Brownfield applications, a slightly different system may be used to the same end.

The inlet to the process is set up in the same way as previously. There are two key differences:

Firstly, instead of using multiple conduits from the process skid or its near vicinity, a single main conduit can be installed leading to the outlet of the process skid, which is used to distribute water containing dissolved gas to any point in the upstream produced water plant.

Secondly a circulating ring-main conduit may be used to distribute the water containing dissolved gas or entrained gas bubbles.

The main conduit is connected to some or all of the water treatment nodes in the produced water plant by way of smaller T-off conduits leading to a manual or automated control valve at each treatment node. The main conduit can either end at the most upstream injection point or it may be re-routed back to the microbubble infusion unit of the process skid to form a ring main conduit. Use of a ring main conduit ensures that pressure is maintained, reducing any gas breakout in the line.

The control valve at each node, reduces the pressure at the point of injection enabling gas to break out to form optimally sized micro-bubbles. The control valve can be adjusted to increase or decrease the amount of microbubble infused water injected into each node, thereby enabling contaminant removal performance to be optimised at that node and/or across the produced water plant as a whole.

It is also possible to inject IGF gas bubbles in the 100 to 1000 pm size. The IGF bubbles are injected into the ring-main conduit as described above, either into untreated water or water already containing dissolved gas, ensuring that optimal gas bubbles size and concentration is maintained.

This enables DGF and two size ranges of IGF gas bubbles to be injected.

Gas flotation in the oil and gas industry is normally injected into relatively low pressure applications. This is in part due to the pressure limitiations of multi-phase centrifugal pumps that are used to generate DGF bubbles using the dissolved gas flotation method. A low-shear centrifugal pump can be installed upstream of the process skid to boost the outlet deliver pressure meaning that high pressure vessels can be targeted. The process will have applications in many other water treatment markets such as municipal, civils and a multitude of industrial applications.

As examples, fluid may be drawn of from point A2 (upstream of the tilted plate separator 123) passed through module 10 to infuse with microbubbles and may be reintroduced at point B2 (upstream of the MP separator 118), point B3 (upstream of the LP separator 122), point B4 (upstream of the HP hydro-cyclone 132) or B5 (upstream of the MP hydro-cyclone 140).

Furthermore, fluid may be drawn from point A6 (downstream of the tilted plate separator 123) and reintroduced at point B6 (upstream of the tilted plate separator 123).

Fluid may also be drawn at point A7 (downstream of the compact flotation unit 165) and injected at point B7 (upstream of the compact flotation unit 165).

Fluid may also be drawn at point A8 (downstream of the degasser vessel 166) and injected at point B8 (upstream of the degasser vessel 166).

Fluid may also be drawn at point A9 (downstream of the produced water settling tank 167) and injected at point B9 (upstream of the produced water settling tank 167).

It will be appreciated that multiple further drawing points A and injection points B may be provided on the described embodiments or on multiple other prior art fluid/water treatment systems and processes. A second embodiment apparatus according to the third aspect of the present invention is depicted schematically in Fig. 4 and generally referred to as 200. This may be substituted for the apparatus 10 described above.

The apparatus 200 may be deployed on a simple skid arrangement to enable transport to and from processes.

An inlet 210 receives relatively clean water from a downstream process point. A pump 212 is provided to create dissolved gas, with the water being transferred along a first pipe 222 to the pump 212. The pump 212 is in the present embodiment a centrifugal multi-phase gas water mixing pump 212.

A pneumatic valve 224 is provide on the first pipe 222 between the inlet 210 and the pump 212.

A feed gas inlet 213 feeds gas to the pump 212 to mix with the water and form the micro-bubbles. A gas conduit 226 transports the feed gas from the feed gas inlet 213 to the pump 212.

The feed gas may be provided from a locally available source, such as exhaust gas or the like, or may be provided from a separate gas cannister or pack.

A gas saturation vessel 214 receives the gas-infused water from the pump 212 via a second pipe 228. A non-return valve 230 and hand valve 232 are provided on the second pipe 228. Gas infused water can be recycled back along a third pipe 215 through to pump 212 to maintain or increase gas saturation and to control injection rate downstream of the gas saturation vessel 214.

Gas infused water is reinjected at an upstream point of the process being treated. A gas infused water outlet 216 from the DGF system is provided which attaches to the process being treated and is fed from the gas saturation vessel 214 via a fourth pipe 234. A pneumatic valve 240 is provided on the fourth pipe 234 provided to control the outlet and reinjection to the process being treated. This is primarily a DGF sized microbubble injection.

In addition, a fifth pipe 217 branches from the fourth pipe 234. A venturi suction device 218 is attached to the fifth pipe 217 which can be used for venturi suction of gas into water, generating microbubbles or can be used for positive pressure gas injection into lower pressure water stream.

A static gas water mixer 219 is attached to the venturi suction device 218 which can be used to cap microbubble size to 300 pm or, if bypassed through bypass pipe 236 enables gas bubbles up to 1000 pm mean diameter. The gas infused water may then be injected at secondary outlet 2112 into the process stream, which contains both DGF and IGF sized bubbles.

The gas feed 2100 for venturi suction device 218 and static gas water mixer 219 may come from the same source as the feed gas inlet 213 which feeds gas to the pump 212 or a separate source may be provided which again may either be provided from a locally available source, such as exhaust gas or the like, or may be provided from a separate gas cannister or pack.

Turning to Fig. 5, a dynamic flotation test unit and method (“DFT”) is depicted schematically and generally referred to as 300.

The DFT 300 apparatus is small enough to fit on a workbench. The primary purpose of the DFT 300 apparatus and method is to establish that there is a positive rise velocity of gas bubble/contaminant agglomerations (as per Stokes law) in opposition to the downward velocity of flow of the main fluid stream in a process upon which the above apparatus and methods may be used. The results can then be compared with calculated velocities for the gravity separation vessels in the current separation system.

Contaminant concentrations are monitored using sample points (not shown) on an inlet line 310 and outlet line 307 of a gravity separation vessel 312.

The downward velocity in a gravity separation vessel 312 is increased until contaminants are pulled down and exit either conduit 307 in recycle flow or through 314 in flow-through operations as evidence by results from the contaminant concentration monitoring.

It is possible to test both IGF and DGF sized bubbles and also to test chemicals to further increase the rate of gas microbubble/contaminant coalescence and therefore rise rate.

A water inlet 301 and gas inlet 302 feed DGF pump 317. The DGF pump 317 outlet of gas infused water is fed into a free gas release saturation vessel 303 via pipe 320. The pump is a multiphase bubble generating pump 317 used to dissolve gas in water.

A surge vessel 305 receives gas infused water from saturation vessel 303 via pipe 304. A recycle line 306 transports water from surge vessel 305 back to water inlet 301 .

A feedline 308 branches off from pipe 304 and therefore from the microbubble generator (comprising the pump 317 and saturation vessel 303) to devices 309. and 18 for generation of IGF microbubbles.

A venturi suction device 309 is fed by feedline 308. The venturi suction device 309 sucks in lower pressure feed gas or may also be used as an injector for higher pressure gas into lower pressure water. A static mixer

318 is fed by the venturi suction device 309 which caps the IGF bubble size to 300pm mean diameter.

Conduit 310 transfers the output of the IGF bubble generator (comprising generally the venturi suction device 309 and the static mixer 318) into a gravity separator 312. The gravity separator 312 includes a skim line. A skimming vessel 313 receives contaminant (e.g. oil) from the gravity separator 312.

A recycle line 307 transfer water from the gravity separator 312 back to surge vessel 305, which then travels through recycle line 306 transports water from surge vessel 305 back to water inlet 301 and onto pump 317.

A main inlet line 311 provides water from a flow-loop recycle line or from once through feed water 319 to the gravity separator 312.

A clean water outlet line 314 for “Once Through Clean Outlet Connection” scenario i.e. to enable the main water flow to be flowed right through as in an offshore production system rather than recirculated from inlet 319 through to outlet at 314.

An oil skim outlet line 315 is provided for once through oil removal from skimming vessel 313.

A heating bath 316 for a recirculation line 324 to simulate temperatures of systems being tested.

DFT 300 apparatus can be operated in flow-through mode with feed water entering at point 319, through a pump 321 , through conduit 311 into vessel 312 with floated oil going to skim vessel 313 and clean water going to outlet 314. Valve 322 is closed and valve 323 is open.

Flow-loop scenario - conduit 311 is the main flow-loop for the gravity separator 312 water. When operating in flow loop scenario flow travels from 319, through pump 321 through conduit 311 into vessel 312, with clean water exiting 312 and rejoining conduit 311 and back through pump 321 to complete the flow-loop cycle. Skimmed oil goes to skim vessel 313 during this operation. Valve 323 is closed and valve 322 is open.

In a further embodiment the microbubble flotation unit is aimed at any oil industry installation which uses tanks for storing and or separating oily water and other solid, liquid and gaseous contaminants arising from production operations, refining operations, drilling operations and from rainwater, deck washings, etc. This includes onshore installations, offshore installations and marine vessels.

Examples of onshore installations include offloading facilities, oil storage facilities, oil production facilities, refineries, water processing facilities, and the like.

Offshore installations include both fixed and floating. Examples include Fixed Platforms, Spars, FPSOs (Floating Production, Storage & Offloading), FSUs (Floating Storage Units), FSO’s (Floating Storage and Offload), MOPUs (Mobile Offshore Production Units), MODUs (Mobile Offshore Drilling Units), Drill Ships, Semi-Submersibles, and various others types.

Oily water is often stored in slop tanks, storage tanks or other types of tank to allow gravity separation of oil, water and other contaminants to take place. Many offshore installations with storage tanks encounter problems when gravity separation isn’t effective and excessive amounts of contaminated water build up in the tanks. The water in the tanks can be treated by infusing the water in the tanks with microbubbles to aid gravity separation using gas flotation. The method is to remove water from the bottom of the tank and inject it with microbubbles, the water can either be transferred back into the same tank or transferred into another tank using transfer pumps and conduit hoses or pipework. A side-steam of contaminated water is taken from the conduit during transfer and passed through a microbubble generator which comprises a centrifugal pump to mix the contaminated water and gas.

The gas flotation process then takes place in the receiving tank, whereby the microbubbles aid flotation of contaminants to the surface of the fluid body. Clean water can be removed from the lower portion of the tank for disposal, or oily water can be skimmed from the top of the tank enabling clean water for disposal.

In a yet further embodiment of the technology a microbubble generator is used to treat Metal Napthenates formation on oilfield fluids. Metal Naptenates cause separation, fouling and deposition problems on offshore installations. Metal Naphthenate precipitation typically takes place at a pH of greater than 6-6.5. This often occurs as a result of Carbon Dioxide being flashed off from fluids as a result of process pressure drops, leading to increased pH.

Reduction of pH can also be conducive to improved oil in water separation where emulsion stability is greater at higher pH.

Reduction in pH can also offset the formation of scale, which causes separation problems and deposition problems in instruments, pipework and vessels.

The prior art is to inject organic acids (such as Acetic Acid) in liquid form into the contaminated liquid to lower the pH sufficiently to prevent problematic levels of precipitation. Scale inhibitors and water clarifiers are also injected to resolve scaling (such as Calcium Carbonate) and separation problems. There is potential for pH adjustment as described above to reduce or eliminate injection of these chemicals.

In this embodiment, a microbubble generator is used to inject Carbon Dioxide infused water into the main water/oil fluid stream or via a sidestream. The Carbon Dioxide can be sourced from bottled gas packs, cryogenic liquid tanks or exhaust gases from combustion or from other Carbon Dioxide rich gas such as upstream separator gas or the main fuel gas system. The micro bubbles can be generated by using a centrifugal pump to mix the gas and water. Gas venturi suction and injection devices can be used to generate microbubbles or small bubbles. The micro-bubble generator skid incorporates a recycle line which enables the Carbon Dioxide infused water to be recycled at a controlled rate allowing the concentration and thereby pH at the skid outlet and in the main process to be controlled to ensure that the pH is sufficiently low to control the precipitation of Naphthenates.

Claims

1 . A method for separating contaminants from a fluid, the method comprising the steps of:

2) Infusing the feed fluid with gas thereby creating microbubbles; and

2. The method according to claim 1 wherein no additional separator vessel is used for the method.

3. The method of any preceding claim wherein no separate uncontaminated fluid supply is used for gas injection.

4. The method of any preceding claim wherein the microbubbles are created in both a DGF and IGF size.

5. The method of any preceding claim wherein the fluid is water.

6. The method of any preceding claim wherein the contaminated fluid is from an oil and/or natural gas process.

7. The method of any preceding claim as applied to an existing oil and/or natural gas process.

8. The method of any preceding claim including a microbubble gasflotation process as follows:

(1) A suspension of micro-bubbles is generated in the fluid;

(2) The microbubbles collide with contaminant particles or droplets;

(3) The microbubbles and contaminants coalesce together to form larger particles or droplets or buoyant agglomerations;

(4) The buoyant particles, droplets or agglomerations then float to a surface of the fluid; and

(5) The surface layer of the fluids can be removed along with the buoyant contaminants.

9. The method of any preceding claim applied to a produced water treatment plant comprising one or more of the following: water treatment equipment, interlinking pipework and sometimes storage tanks and vessels (such as gravity separators, gas floatation units, hydrocyclones, dissolved gas flotation units, collection vessels, plate separators, settling tanks, settling ponds, surge tanks, other vessel types, other water treatment devices) wherein fluid is taken from an upstream point of the plant, injected with separating gas and the fluid/gas mixture reintroduced into a upstream point of the process.

10. A method of modifying an existing fluid contaminant separation system which includes one or more contaminated fluid inlets, and one or more fluid outlets comprising the steps of:

(1) draining an at least partially decontaminated fluid at a first point between the one or more fluid inlets and one or more fluid outlets;

(2) injecting a separating gas into the at least partially decontaminated fluid;

(3) injecting the separating gas treated at least partially decontaminated fluid into a second point on the existing fluid contaminant separation system; wherein the first point is downstream of the second point.

11 . The method according to claim 10 wherein there are one or more upstream points where the separating gas/partially decontaminated fluid mixture is injected in addition to the second point.

12. The method of claims 10 or 11 wherein no additional separator vessel is used for the method.

13. The method of any of claims 10 to 12 wherein no uncontaminated fluid supply is used for gas injection.

14. The method of any of claims 10 to 13 wherein the fluid is water.

15. The method of any of claims 10 to 14 wherein the contaminated fluid is from an oil and/or natural gas process.

16. The method of any of claims 10 to 15 as applied to an existing oil and/or natural gas process.

17. The method of any of claims 10 to 16 including a microbubble gasflotation process as follows: (1) A suspension of micro-bubbles is generated in the fluid;

(2) The microbubbles collide with contaminant particles or droplets;

18. The method of any of claims 10 to 17 applied to a produced water treatment plant comprising one or more of the following: water treatment equipment, interlinking pipework and sometimes storage tanks and vessels (such as gravity separators, gas floatation units, hydrocyclones, dissolved gas flotation units, collection vessels, plate separators, settling tanks, settling ponds, surge tanks, other vessel types, other water treatment devices) wherein fluid is taken from an upstream point of the plant, injected with separating gas and the fluid/gas mixture reintroduced into a downstream point of the process.

19. Apparatus for carrying out any of the methods of any preceding claim comprising one or more fluid inlets, one or more fluid outlets, one or more separating gas inlets, and a gas/liquid mixing pump wherein the one or more fluid inlets and one or more separating gas inlets are connected to an inlet side of the gas/liquid mixing pump and the one or more fluid outlets are connected to an outlet side of the pump.

20. Apparatus according to claim 19 wherein there are two gas/liquid mixing pumps, one being IGF and one being DGF.