Decanter centrifuge effective with all types of drilling mud

Alfa Laval chose Houston's OTC exhibition as the venue for launching its new Lynx 40 drilling fluid separator.

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The new Lynx 40 decanter centrifuge features slender rotors with the liquid discharge weirs placed at a much smaller radius than on conventional decanters, resulting in low power consumption and lower investment costs.
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Alfa Laval chose Houston's OTC exhibition as the venue for launching its new Lynx 40 drilling fluid separator. The company believes that this new addition to its range of decanter centrifuges will bring important benefits for users seeking lower investment costs, while also seeking high separation performance combined with low power consumption.

The Lynx 40 is the second in a new series of decanter centrifuges from Alfa Laval Oilfield. It follows the introduction of the slop oil decanter the Lynx 30 recently to provide an effective solution for the separation of solids and liquids in the recovery of slop oil. Both decanters are equipped with very slender rotors with the liquid discharge weirs placed at a much smaller radius than on conventional decanters. This means lower investment costs for the machines as well as much lower power consumption. The settling area for separated solids is also larger than on centrifuges with short, thick rotors, resulting in higher efficiency while maintaining the same flow rate.

The Lynx 40 was designed and tested for liquids/solids separation in the drilling applications market. It has a maximum throughput capacity of 100 cu m/hr, a nominal flow rate of 60 cu m/hr and a nominal solids capacity of 12 tons/hr. The solids cut size for this machine is around 2 microns. Adapted for classified areas, it is fully erosion protected for round-the-clock operation. The hinged rotor hood is easy to open and the liquid discharge weirs are adjusted from outside the rotor for quick choice of pond depth.

Speed control

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The decanters in the Lynx series are optimized to convey low friction solids typically found in chemical gel-type drilling fluids. This gives it the advantage of remaining effective even if changes in the drilling operation demand use of a mud with different characteristics. The dryness of the solids phase and the clarification capability are maintained at optimum levels, unaffected by variations in the flow or composition of the feed. This is achieved by means of an automatic differential speed control system which automatically regulates the differential speed of the screw conveyor to the value set by the operator. It also incorporates the direct drive motor connected to the sunwheel of the gearbox. - The Hydroflokk process features a conditioning reactor vessel that uses droplet coalescence and flocculation to enhance oil from water separation in hydrocyclone separation systems. It can achieve consistent water quality of 10-15 ppm concentration of oil.

By varying the speed of the motor, the speeds of both the sunwheel and the screw conveyor are infinitely variable. The differential speed is consequently minimized which means that wear on the screw conveyor is reduced. Since it is possible to change the rotor speed and the torque over a wide range, the Lynx 40 enables flow rates to be controlled precisely and the separation characteristics to be varied to suit the mud. It is capable of delivering full torque at low speed.

The LYNX 30 differs in that it is built for a slop oil recovery application and is optimized to convey low friction sludges typically found in slop oils. The dryness of the solids phase and the clarification capability are kept continuously at optimum levels, even when there are fluctuations in the flow rate or composition of the feed. It has a maximum throughput capacity of 60 cu m/hr, a nominal flow rate of 30 cu m/hr, and a nominal solids conveying capacity of 3,000 l/hr, or 6 tonnes/hr. Solids cut size for the machine is in the region of 2 microns.

All Alfa Laval centrifuges are designed to work at highly optimized efficiencies. Performance is critical for reducing or eliminating the use of process chemicals. This is especially important for applications such as produced and oily water treatment, where an extremely high quality product is required for marine disposal. Highly efficient disc stack centrifuges are designed for this purpose, and may be installed as complete, compact, fully integrated separation systems.

Hydroflokk

In addition to the environmental benefits, significant savings are realized through reduction of conventional treatment chemicals. A further Alfa Laval development in this regard is Hydroflokk, which features a conditioning reactor vessel that uses the combined principles of droplet coalescence and flocculation to enhance oil from water separation in hydrocylone separation systems. The function of de-oiler additives is totally optimized, resulting in high efficiency and lower consumption. Sometimes their use is not required at all as the mechanical action of Hydroflokk may achieve the purpose alone. Hydroflokk systems are currently installed on both the Troll B and C platforms, where they are working successfully.

The Hydroflokk vessel comprises two separate, interconnected chambers. Each contains a specially designed mixer operating at low speed, intended to optimize the processes of oil droplet growth. Produced water from the upstream production system flows into the first chamber, designed to promote coalescence. When requ-ired, a coagulant may be dosed into the water via a static mixer before entry to the chamber.

The coalesced water then flows into the lower chamber where the function is to flocculate the enhanced oil droplets to form robust "flocs," or suspended agglomerates. The flocs then pass onward to the hydrocyclones, which are able to separate them more effectively due to their acceptable size. One especially important feature of the Hydroflokk environment is that it can be optimized to present strong oily flocs, sufficiently stable to resist the shearing effects sometimes experienced at the hydrocyclone inlet.

Hydrocyclone boosting

Hydroflokk may be retrofitted to existing hydrocyclone systems in order to boost performance, It is particularly useful to operators seeking to improve their water discharge quality ahead of anticipated legislation demanding reductions in oil disposal levels.

Alfa Laval also offers a solution to the handling of oily reject streams resulting from produced water processes. Rejects contain high concentration of oil, solids and chemicals. They are frequently returned to the main process separators via pumps which create highly sheared, stable emulsions. Recycled into production vessels, the emulsions inhibit mainstream separation processes and build up interface pads inside the separators.

As an alternative to recycling, the reject streams can be processed directly in a disc stack centrifuge. This process requires only a small vessel modification, allowing collection of the combined rejects in the oil compartment of a degasser, or flash tank. This troublesome stream can be fed into a single centrifuge, sufficient for most reject proportions. The centrifuge separates it into clean, disposable water and an oil stream of sufficient dryness for blending directly with the export oil. No reject recycling means no emulsion accumulation and no detrimental effects on the upstream process.

New, improved produced water treatment systems use both the Hydroflokk and a rejects centrifuge in combination. The benefits are reduced chemical cost, improved efficiency, flexibility and the ability to achieve consistent water quality of 10-15 ppm concentration of oil, even for difficult treatment cases.

For more information contact Daniel Knapper, Alfa Laval Oilfield Division. Tel +44 1224 647222, Fax +44 1224 626866, Email: daniel.knapper@alfalaval.com

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