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Water Treatment |
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Water Treatment
- Oil Removal Cyclones
- Induced Gas Floatation
- Nut Shell Filters
- CPI Units
- Spare Parts and Retrofits
- Magnetic Descalers
- Site Testing and Surveys
As oil fields are produced and depleted, water production typically increases up to 100% of the well’s output. This water must be processed and discharged in compliance with stringent environmental legislation – all while operators strive to maintain their production targets. This is an onerous task for aging fields that produce far more water than oil, and that are usually delivering ever decreasing oil revenues.
A successful and reliable Produced Water Treatment system typically includes the following key elements:
- Primary Separation: bulk oil and solids removal
- Secondary Separation: additional oil and solids removal
- Tertiary Treatment: final polishing, which may be required for specific conditions or difficult applications
It is common for plant design to be based on more than one single element or treatment process. For most applications, the Primary bulk oil removal stage is vital to reduce the oil loading on the Secondary (and Tertiary, where applicable) water polishing equipment to meet the water discharge target.
Deoiling Hydrocyclones
Deoiler Hydrocyclones were developed for the offshore oil industry in the 1980's. They rapidly became standard equipment used for oil recovery from Produced Water streams. Deoiler Hydrocyclones deliver the following benefits:
- Compact design, replace substantially larger equipment
- Cost-effective with low OPEX costs
- No moving parts and little maintenance required
- Highly consistent performance
- Proven technology
- Suitable for use on FPSO's, etc.
Description
Deoiler Cyclones are used to recover liquid hydrocarbons from oily-water streams. The Cyclones are mostly installed in a pressure vessel in a cluster, with the required number (1-270) of Cyclone Liners to match the water flow rate.
Cyclone Liners are made in a range of sizes, (40-70 mm diameter) and are constructed from Duplex Stainless Steel to provide maximum durability and corrosion resistance. As shown below, the Deoiler Cyclone Liners are installed into the vessel by hand and can be removed for inspection. Liners or Liner Blanks can also be added with simple hand tools. Liner Blanks are used where the water rate may begin at a low rate and increase over time. Liners can be added or removed to match fluctuating water rates.
Operating Principles
Deoiler Cyclones are driven by inlet water pressure and utilise a pressure drop across the Cyclone to provide the energy or driving force to cause oil-water separation. Normally, system pressure is used to provide the driving pressure, but if it is too low (<60 psi / 4 Bar), a pump can be used to boost the feed pressure. Typically, single stage centrifugal pumps are used where pressures are too low.
Each Cyclonixx® Deoiler Cyclone Liner includes a tangential Inlet Section where the water enters and is forced to spin rapidly, generating high centripetal forces. These forces, combined with the tapering shape of the internal profile, accelerate the spinning. This effectively forces the water away from the centre axis to the outer walls, and forces the lower density oil to the central core that forms along the axis of the Deoiler Cyclone.
The water spirals down the tapered section of the Cyclone and exits via the clean Water Outlet nozzle. The central oil core is forced in the reverse direction by back pressure on the Water Outlet, and exits via a small orifice, the Oil Reject Outlet. The Oil Reject stream flow is largely controlled by this orifice's size, but can also be regulated by an outlet control valve that is typically set to allow a flow at 2-4% of the inlet flow.
The gravitational forces generated within each Cyclonixx® Deoiler Cyclone Liner are very high. Therefore, Deoiler Cyclones can be installed vertically, horizontally or on moving structures (e.g., FPSO's).
Technical
There are a few important factors involved in the process design and selection of a Deoiler Cyclone Liner type. They are:
- Available pressure/pressure drop
- Oil droplet size and distribution
- Liquid viscosity/temperature
- Cyclone diameter and required oil recovery
Available Pressure /Pressure Drop
It is usually preferable to utilise the full system pressure to drive Deoiler Cyclones to maximise oil recovery and throughput. The preferred site to locate cyclones in a process is on the water outlet line from the Separator or Water Knock-out Vessel upstream of the Level Control Valves. This usually provides the highest capacity with minimal droplet shearing.
The operating pressures for a Cyclonixx® Deoiler Cyclone are defined by the Pressure Differential Ratio (PDR). The PDR is defined as:
Where:
P.Inlet = Pressure at inlet of Deoiler Cyclone
P.Reject = Pressure of Reject oil stream outlet
P.Outlet = Pressure of Water Outlet stream
PDR should be maintained in the range of 1.7 - 1.8.
Pressure Drop versus Flow for one XL-40 Cyclone Liner
A graph depicting the effect of increasing pressure drop is shown below, with Pressure Drop versus Flowrate for an XL-40 Deoiler Cyclone Liner.
Note: the above graph is for one type of Deoiler
Process Group manufactures a number of cyclones as Spare Parts for most common brands of Deoiler Cyclones.
Oil Droplet Size /Distribution
The Oil droplet size range has a major impact on the Deoiler Cyclone's performance. It is important to maintain as little shearing of oil droplets as possible prior to the cyclone by installing upstream of control valves to avoid excessive droplet shearing.
Liquid Viscosity/Temperature
Temperature has a direct effect on the water viscosity, which has a significant effect on the cyclone's performance. At higher temperatures the water viscosity is reduced, creating less resistance to the separation of oil droplets. Higher temperatures will result in higher levels of oil/water separation.
Cyclone Diameter/Performance
The effect of the diameter of the Deoiler Cyclone Liner on oil and water separation is very important. Smaller diameter cyclones provide higher levels of oil removal, but they have a lower capacity. To compensate for this multiple Cyclone Liners are packaged inside each vessel to treat large flows, while maintaining high oil-removal levels.
Deoiler Unit Sizing
Process Group provides a range of Deoiler Cyclone Vessel sizes, but the following provides a helpful guide for typical vessel capacities.
Deoiler Cyclone Vessel Size on Flowrate.
Deoiler Cyclone Vessel
Size on Flowrate
Project References and Case Studies
Process Group has successfully completed a wide variety or projects all over the world working with governments and name companies. Read the case studies below to learn more about some of our water treatment projects and the technical solutions and value we delivered.
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