Centrifugal Separation Technology for Water Treatment in Oil & Gas Industry
Article Courtesy : Alfa Laval

Treatment of produced water poses challenges for oil and gas producers. There are many technologies are available, and it is not easy to know which technology is best suited to the task at hand. The volumes and composition of produced water vary significantly, depending on numerous factors. Often several technologies are used in combination, along with the addition of process chemicals, to treat produced water due to changing properties in terms of a broad range of contaminants and their varying concentrations. The white paper aims to familiarize engineers working on oil and gas rigs and floating production storage and offloading (FPSO) vessels with centrifugal separation technology as a compact, effective and often chemical-free alternative to conventional technologies.

Produced water is an integral part of, and often the largest volume waste stream associated with, oil and gas production operations. Due to increasingly stringent regulations, produced water requires extensive treatment before discharge into the environment. The varying volumes and composition of produced water, with frequent re-routing of reject streams and high chemical dosing, make treatment complex. Many oil and gas producers are often looking for solutions that simplify produced water treatment.

When faced with complex produced water compositions, many oil and gas producers find that they have difficulty treating produced water effectively with conventional technology. To achieve performance that complies with environmental regulations, global players and local oil and gas producers have approached Alfa Laval to gain a better understanding of centrifugal separation technology, its capabilities and performance track record in treating produced water both offshore and onshore.

Centrifugal separation technology is proven, robust technology widely used in the marine industry to treat hard-to-handle oily waste streams. It effectively separates these streams into oil, water and solids that comply with environmental regulations for safe discharge and/or disposal.

However, it is a technology that is not well-known or widely used within the oil and gas industry. That said, oil and gas producers familiar with the use of high- speed separators for onshore processes have used the technology offshore to treat produced water with success for the past 30 years.

Despite the reser vations of oil and gas producers to use technology with moving parts, the Alfa Laval centrifugal separators have proven robust, reliable, effective and easy to maintain when used for produced water treatment. It is important to note that, when using high-speed separators to treat produced water, there is generally no need for pretreatment such as heating or chemical dosing.

There are also no reject streams to route back to the treatment system. Plus the compact size and weight of centrifugal separators make them ideal for use on new offshore installations or as retrofits on existing installations.

The aim of this Alfa Laval white paper is to address the most frequently asked questions raised oil and gas producers. Oil and gas producers are struggling with conventional technologies and are considering the use of centrifugal separation technology to treat produced water on offshore installations. By sharing insights into why centrifugal separation is a sound choice for treating produced water, we hope that oil and gas producers who struggle to comply with increasingly stringent environmental regulations may consider centrifugal separation as an alternative to conventional produced water treatment methods.

Centrifugal Separators in Oil and Gas Field Applications
Does centrifugal separation technology perform differently when used in oil field applications versus in gas field applications?
Generally speaking, there is no discernible difference in performance when using high-speed separators in oil field applications or in gas field applications. Gas field applications, however, are somewhat more challenging because the size of the droplets in the oil fraction tend to be smaller and more stable than those found in oil field applications. Below is an over view of the performance of Alfa Laval centrifugal separators when in various oil field applications and gas field applications.

Polishing/tertiary treatment
The performance of Alfa Laval centrifugal separators is essentially the same whether used in applications in oil fields or gas fields. It is important to note, however, that produced water generated in gas fields tend to contain droplets of dispersed oil that are smaller in size compared to droplets generated in oil fields. This is primarily due to greater pressure drops and different well chemistry found in gas fields. Condensate is more easily dispersed in produced water by shearing due to low interfacial tension. In addition, the low interfacial tension reduces the coalescence of the dispersed droplets, resulting in the formation of more stable emulsions.

While these smaller droplets pose a greater challenge to conventional produced water treatment equipment, they are well within the operating range of centrifugal separators, which can easily remove small droplets in the range of 1–10 microns in size. To handle difficult cases with significantly smaller droplets, centrifugal separators require minor adjustments to enable the effective removal of oil droplets; this includes a reduction in flow rate and a slightly longer residence time - typically from one to two seconds or from two to three seconds.

Conversely, if conditions improve, the higher separation efficiency due to the larger droplets can instead be used to shor ten the residency time and achieve higher capacities. This was the case at the Woodside North Rankin A (WNRA) gas field in Australia. WRNA has long operated at a pressure drop from the well of approximately 100 bar. At this pressure drop, shear forces generated small droplets that an Alfa Laval highspeed separator removed at a flow rate of approximately 29 m3/h. Due to recent process changes, the pressure drop was reduced to 50 bar. As a result, the positive effect of less shear generates larger droplets, enabling an 28% increase in separator capacity, from 29 m3/h to 40 m3/h while maintaining separation efficiency or the same low levels of oil-in-water after treatment. In addition, residence time was reduced by 25%, from 2 seconds to 1.5 seconds.

Centrifugal separators are used in primary treatment polishing of reject streams. Ter tiary treatment, in this context, is understood as salt removal , which is not common for centrifugal separators in produced water treatment because salt normally does not precipitate from the streams. It is important to note, however, that any precipitated salt will be removed in a high-speed separator. Separators, for instance, are used offshore to remove small salt precipitates that are less or much less than 10 microns in size from monoethylene glycol (MEG) streams. An Alfa Laval centrifugal separator tested on a floating liquefied natural gas (FLNG) vessel to remove precipitated salt from MEG streams resulted in effective removal of salt par ticles down to 0.8 micron in size.

Dispersed and dissolved oil removal
A mechanical piece of equipment, a centrifugal separator only removes dispersed oil while simultaneously removing suspended solids. It does not remove dissolved oil. While the focus of produced water treatment tends to be on dispersed oil removal, it is important not to overlook the positive effects of the simultaneous removal of solids. Increasingly, oil and gas producers are focusing on solids management in many installations because fine solids stabilize small oil droplets. These fine solids pose challenges when re-routing reject streams back into conventional produced water treatment processes; the presence of solids in the reject streams make the overall performance of the system worse. This is not an issue in produced water treatment systems using centrifugal separators; solids are either intermittently or continuously discharged from separator for disposal and therefore do not negatively impact the system's performance (Figure 1).

Fig 1

Produced water
Not only are centrifugal separators used to treat produced water, but they are also used to treat other oily water streams in various processes during oil and gas production. Sometimes produced water is called slop water, which is the term typically used on floating production storage and offloading (FPSO) vessels where the volumes of produced water are not significant. FPSOs may, in some installations, accumulate all produced water in a tank and then feed the water into a centrifugal separator. FPSOs may also have a conventional produced water treatment system in place, but also may collect streams from other areas, such as a tank that is subject to upset conditions , and then process these streams as slop water in a separator. Around the globe, Alfa Laval centrifugal separators treat slop water from processes on board FPSOs as well as bilge water on board marine vessels.

When using centrifugal separators, there is essentially no difference in performance between the treatment of slop water and the treatment conventional produced water; in most cases, the use of centrifugal separators results in treated water that contain between 2 to 15 ppm of oil -in-water, which can be discharged overboard in compliance with environmental regulations.

It is notable to draw an analogy between treating slop water on board FPSOs and treating oily water on board ships, where more than a 1,000 Alfa Laval PureBilge centrifugal separation systems are in operation worldwide. Certified by the International Maritime Organization (IMO), the Alfa Laval PureBilge system can effectively reduce the oilin- water content of bilge water with varying feed conditions to less than 5 parts per million (ppm).

Centrifugal separators are also used to treat oily water from various drains. The toughest application is drill deck drains, where separators alone are not suitable due to very high solids loads and the emulsifying additives used for mud. For successful treatment of tough applications such as these, treatment systems typically comprise decanters for solids removal, flocculation for chemical removal and band screen filtration, and separators for final polishing.

Typical configurations
There are various configurations for treatment systems using centrifugal separators. Separators may be selected as the sole piece of mechanical treatment equipment for a conventional degassing train, together with between one and three 3-phase static separators. More commonly, separators are used as a part of a produced water treatment system, together with hydrocyclones, a degasser or induced gas flotation (IGF) unit, and compact flotation unit (CFU) or similar. The process solutions, where centrifugal separators are an integral part of a system, have the advantage of processing higher volumes of water at higher flow rates, while at the same time minimizing capital expenditures (CAPEX) as well as the number of separators required (Figure 2).

Fig 2: Conventional produced water treatment system: Troublesome reject streams are typically re-routed back into the process, thereby creating process issues.

Above all, centrifugal separators make it possible to avoid re-routing reject streams into the produced water treatment tank or crude dehydration process. Many system designers of these conventional processes often, and in fact almost always, re-route reject stream in the hopes that the flow rates are so small that the separation issue will somehow resolve itself. The use of a centrifugal separator effectively does away with the need to re-route reject streams.

Rerouting reject streams tends to cause process disturbances elsewhere by introducing small, often stabilized, oil droplets back into the process. These droplets have often been stabilized by small par ticles, waxes, corrosion-inhibitor chemicals and other means. Over time, the droplets collect in emulsion layers that build up inside the static separators. This not only results in poor separation performance, but also makes level detection and process control very difficult.

The most common system configurations for avoiding poor reject stream treatment are illustrated on Fig 3, 4, 5, and 6.

Fig 3: A traditional HC/CFU process

Fig 4: Installation used on Tyra platforms, where the water flow from the separator train is taken into a surge tank and fed into a centrifugal separator for treatment to obtain discharge specifications

Fig 5: Proposal for oil platform: Full-flow treatment of produced water with centrifugal separators. In installations built on separators for both oil treatment and water treatment, the separators can be converted from oil to water treatment as the water cut increases over the lifetime of the field.

Fig 6: Typical installation using hydrocyclones for bulk flow and treatment and a centrifugal separator to treat reject streams to safeguard the total separation train and treat the more troublesome oily water streams. This type of installation is used, for example, at Ekofisk in the North Sea.

Many operators spend a lot of time tr ying to resolve separation issues that turn out to be related to the effects of re-routing. Rerouting only makes the separation task much more difficult. Numerous offshore installations struggle to treat their produced water properly. Hydrocyclone reject is often denominated as "oil" being returned into the process, but the reject stream can easily contain up to 95% water. Another issue is very low efficiency in installations using hydrocyclones at low pressure separation. Sometimes a pump is installed to increase pressure upstream of the cyclones, but this pump normally also contributes to the formation of smaller droplets and poor separation efficiency.

Finally, there are always solids in the crude oil stream from a well. This is not taken into consideration in the typical configurations shown here. Fine particles from the formation precipitate out of the stream and collect at various stages in the process. Eventually, sedimentation must be physically removed from, or dug out of, various locations, like the static separation tanks. The par ticles range in size down to microns; some of these small particles adhere to the surface of the oil droplets, stabilizing them and preventing coalescence of small droplets into larger droplets, which is necessary in order to remove the oil from conventional process streams.

Centrifugal separators, on the other hand, deliver high separation efficiency and operate ‘once through’; no rerouting of reject streams is required. When a process operates at higher pressures, a degasser is generally required. Some centrifugal separator models are able to handle pressure of 4-6 bar. However, most models operate at atmospheric conditions.

Centrifuges used in different ways
The most common system configurations for avoiding poor reject stream treatment are illustrated below.

Greenfield and brownfield projects considered
The advantages of using centrifugal separators for greenfield and brownfield projects are similar, but also somewhat different. Brownfield projects tend to have stringent regulations that require compliance. Here centrifugal separation technology can drastically improve performance compared to the conventional technology t ypically used in existing greenfield and brownfield processes. Improvements to overall processes include doing away with the need to reroute reject streams and/or polishing the most difficult streams to specifications. Compact and lightweight, centrifugal separators generally meet the space and weight constraints of brownfield projects. Below is an over view of centrifugal separator capacities, sizes and weights.

For greenfield projects, centrifugal separation technology reduces CAPEX by minimizing the footprint of the produced water treatment system and thereby reducing installation costs. Holdup volumes in centrifugal separators are negligible compared to static separators. Large centrifugal separators, capable of processing 190 m3/h, offer a separation area equivalent to some 200,000 m2 when compared to static equipment, but only require 70 litres of holdup volume in the separator bowl, and a residence time of two to three seconds. The entire centrifugal separator module uses only 6.6 m2 of deck space and weighs just eight tons.

System Integration Aspects

What are the considerations for inventory management for the centrifugal separator?
Inventory management considerations can be divided into two parts: the first revolves around the cleanliness of the bowl and maintaining the highest separation performance over time, and the second focuses on uptime, maintaining the mechanical integrity of the separator as well as its drive /spindle.

With regard to bowl cleanliness, separators operating on produced water tend to require cleaning of the disc stacks at regular intervals. These inter vals range from several months to several years, depending on various factors. Disc stack cleaning has generally been resolved by Cleaning-in -Place (CIP), by manual cleaning of the disc stack offshore, or by replacing the offshore disc stack and/or bowl while sending the dirty disc stack/bowl for cleaning ashore.

Inventory management considerations typically address keeping a spare disc stack on hand and possibly adding a spare bowl to the inventory. Alfa Laval generally recommends keeping a spare disc stack in stock on site rather than keeping a spare bowl in stock to minimize inventory costs. Replacement of the separator bowl requires complete disassembly of the bowl; the disc stack is one component of the bowl, which means that there is no difference in time savings when replacing the bowl.

The advantage of bowl replacement lies in the ease in operation.

When using a separator with intermittent discharge capabilities, the discharge systems that operate using fresh water should be checked and/or cleaned when replacing the disc stack. In an effort to save time, operators responsible for replacing the disc stack do not always inspect and/or clean the discharge system. Over time – sometimes months or years, the discharge system may pose issues because the quality of freshwater offshore that is used as operating water varies greatly.

An impor tant aspect of inventory management relates to installed redundancy . Oil and gas producers seem to approach redundancy for produced water systems in different ways; the most common approaches are 2 x 100% and 3 x 50%. Redundancy secures oil and gas production uptime as well as adds greater flexibility to produced water treatment as the standby unit can be put into operation when required. This provides oil and gas producers with greater flexibility to cope with unforeseen events that result in upset conditions. During such conditions, deploying additional centrifugal separators at reduced flow rates can help oil and gas producers continue to treat produced water while complying with environmental regulations. Longer residence time in the separators - even if only seconds longer - further improves separation (see page 13 on droplet size distribution) and helps ensure that the oil-in-water content meets regulations for overboard discharge.

In Alfa Laval's experience, deploying redundant separators is a treatment strategy that is rarely used, mainly due to the operators' limited understanding of its functionality and how to make the best use of centrifugal separation technology.

With regard to aspects of mechanical integrity, inventory management strategies vary depending on the installation. With maintenance routines in place, there is generally no need to keep a spare spindle or other drive parts in stock. Centrifugal separators generally have long service lifetimes. Many installations using centrifugal separation technology have been in operation for more than 20 years. However, for installations where produced water treatment capabilities are extremely critical, keeping a spare spindle on hand should be considered.

Finally, any inventory management strategy for centrifugal separators should include stocking Alfa Laval Service Kits for separators for use at intermediate service and major service intervals. The recommended interval for intermediate service is every 2,000 hours of operation depending on the operating conditions; some models have longer intervals. Major service is recommended once a year, or every 8,000 hours of operation; this entails more comprehensive maintenance, including bearing replacement. Although fast global delivery of standard service kits is available, Alfa Laval highly recommends that oil and gas producers using centrifugal separators at offshore installations stock these kits on site.

Many oil and gas producers consider centrifugal separator maintenance a disadvantage compared to using conventional static produced water treatment technologies. In the past, offshore studies reported that rotating equipment maintenance was a concern. Overcoming these concerns requires a change of mindset. The offshore industry perceives the operation and maintenance of centrifugal separators as complex. However, just the opposite is true for other sectors of the oil and gas industry and other similar industries.
  • In the tar sands in Canada, the most challenging onshore oil production environment, Syncrude has been operating a massive centrifugal separator installation for decades with a challenging and erosive feed that requires high maintenance. With a positive attitude and solid training, the Syncrude maintenance team conducts routine maintenance and keeps the equipment in good working order to ensure high performance and high production.
  • In the shipping industry, there are more than 50,000 merchant ships in operation. All are equipped with centrifugal separators that have maintenance requirements similar to those operating at offshore installations. Ship maintenance routines are an integral part of crew duties and maintenance is performed accordingly, even though the crews on ships tend to be less well educated than those working in offshore production.
Maintenance of separators at offshore installations has the potential to work equally well. Some major North Sea operators that have a significant installed base of centrifugal separators provide training on regular basis to ensure their staff can operate and maintain the equipment. Repeat training is another way to ensure the right attitude and competencies are maintained among personnel over time due to the inevitable and gradual loss and replacement of employees over time.

Alfa Laval has noted that operators at many offshore installations tend to push separator performance beyond the operating limits of the equipment. This is due to the robust, reliable performance of the separators. Operators soon realize that centrifugal separators can cope with wide variations in operating conditions, particularly when troublesome streams are fed into the separators to try to solve operational problems temporarily. In these situations, employees put the separators to work - due to lack of training or lack of understanding about how separators work - without making the necessary adjustments to the flow rate, discharge inter vals and other operating parameters. This often results in separators filling with sediments; when maintenance is then required, operators tend to view these events as equipment failures due to upset conditions rather than human error.

What pretreatment methods, if any, are required when using centrifugal separation technology?
Unlike conventional produced water technologies which require various pretreatment methods, centrifugal separators only require a strainer upstream to prevent oversized material from entering the separator. Such material may be anything ranging in size from large items, such as gloves, welding pins and tools, to large par ticles. A strainer with a 0.5 mm mesh is recommended to prevent particles larger than this size from entering the separator and adhering to distribution channel sur faces inside the disc stack; over time, these particles will block the flow and have a negative impact on the performance of the separator. If a specific installation does not use standard spacing between discs in the stack , the mesh size of the strainer may be slightly smaller or slightly larger (0.4-0.6 mm). In produced water streams with high solids loads and the use of a continuous- discharge separator with nozzles, the nozzle diameter determines the mesh strainer size. The nozzle size selec tion is based on the solids content; a mesh size that is approximately one -third the size of the selec ted nozzle size is recommended.

To further improve performance, there are some areas to consider, which contribute to higher separation efficiency. Using a pump that provides gentle pumping action to feed produced water into the centrifugal separator contributes to higher separation efficiency. This prevents oil droplets from splitting when fed into the treatment system.

A separator readily copes with small oil droplets in water; however, to improve performance and/or capacity when separating larger droplets, it is important to take these factors into consideration:
  • Heat. Heat has less impact on viscosity in water compared to oil. Even if the water has a low viscosity from the start, the reduction in viscosity through the use of a heater is negligible. Heat tends to improve separation performance; however, it is not necessary to install a preheater before a separator to achieve good separation efficiency.
  • Chemicals for flocculation or coalescence. Unlike many produced water technologies that have difficulty handling small oil droplets and therefore require demulsifying chemicals, separators do not require chemical additives to treat produced water. However, as with any treatment equipment, the use of demulsifiers provide an opportunity to further improve performance. It is important to note, however, that centrifugal separators generally offer the possibility to treat produced water by reducing or eliminating chemical consumption.
What is the waste management impact with respect to quality, quantity, integration/treatment?
The key waste stream from a separator operated in a produced water treatment system is the separated solids stream. In most installations, this stream is remixed with the water discharged overboard, as the amount of oil attached to solids is still within discharge specifications. Before the solids are discharged from inside the centrifugal separator, they pass a zone of produced water that has been separated from oil. The volume and quality of solids, in terms of oil contamination, generally allow the solids to be remixed with produced water for discharge overboard. In some regions and/or installations, this solid rich stream is collected in tanks and shipped for waste treatment at onshore facilities. This volume of solids is small compared to a produced water stream. Alfa Laval has equipment to further reduce the solids waste stream into solids with higher dryness, but so far this solution has not been requested for use offshore.

The separated oil stream is not generally considered to be a waste stream. The water content in the separated oil may often be as low as 1-2% and up to 20% in the toughest conditions. Because this stream is relatively small, it can be blended into the produced oil without impacting the quality of the produced oil. This is a critical difference between the performance of a separator and a conventional produced water treatment system. Using separators does not require rerouting reject streams to the water stream as conventional systems do (mentioned earlier in the ar ticle).

Finally, with regard to impact on offshore waste management, it is important to note that a centrifugal separator generally does not have any consumables, such as filters. The waste generated from operating a separator amounts to the small number of seals (o-rings) inside the process wetted bowl that must be replaced according to the recommended service schedule. Other waste material includes bearings that have been replaced, usually on an annual basis during maintenance, and a few litres of lube oil from annual lube oil replacement.

How does gas flashing from the produced water stream in the feed influence centrifugal separator performance?
Flashing inside the centrifugal separator does impact performance unless flashing is relatively limited. The effects of flashing are somewhat dependent the model of separator. In conventional models, so-called topfed separators, the feed inlet is a static tube that leads into the centre of the rotating separator bowl. The water stream is usually depressurized in inlet zone, although sometimes it is depressurized before the inlet zone. Any significant gas release will cause internal overflow in the acceleration zone (the distributor), and eventually contaminate to some extent the outgoing produced water that has been treated. To prevent contamination due to flashing, depressurization before the separator is recommended. It is also possible to select a separator that allows operation of the rotating bowl with process liquid at pressures of up to 4 bar g, thereby preventing the release of gas from the produced water. Alfa Laval also has other separator models designed with an enclosed feed/acceleration zone, known as 'centre-to-centre' design. These models keep the liquid under pressures of up to 6 bar g, which prevents the release of gas from the produced water.

What other factors may impact separator performance?
Other factors that may have an impact on separator performance include production chemicals, corrosion inhibitors and the presence of heavy oil in produced water.

Production Chemicals
In general, chemicals used in conventional treatment systems to treat produced water tend to create and stabilize smaller oil droplets, making produced water treatment more difficult. This not necessarily true for treatment of produced water using centrifugal separators. Centrifugal separators are better equipped to remove small droplets; however, separators may experience poor performance when subject to extremely poor operating conditions. If a separator is sized to meet a performance target based on a specific oil droplet size distribution, for example, Dv50 = 15 microns, and the production chemicals generate a Dv50 value of 5 microns, it will be necessary to reduce the capacity of the separator in order to meet the performance target.

However, reducing separator capacity may not be possible, depending on the design of produced water system with regard to redundancy or spare capacity. Fluid proper ties from the production chemicals can have a negative impact on separation efficiency in conventional treatment systems including static separators, hydrocyclones, CFU units. In all likelihood, this means that the capacity of a downstream reject treatment separator is no longer sufficient.

Corrosion Inhibitors
Corrosion inhibitors have two mechanisms that are particularly relevant, which are related to their ability to create oil-wetted par ticles, where the apparent density becomes similar to water. The first mechanism is their ability during the production process to reduce the surface tension of the oil droplets, from about 30 dyne/cm to about 10–20 dyne/cm. This makes it easier to break up the droplets into smaller droplets due to a reduction in pressure. As described earlier, small droplets are more difficult to separate, but also are more difficult to coalesce into larger droplets. The situation is further exacerbated by the surface charges caused by these surface-active chemicals, which also stabilize the droplets and, consequently, aid creation of emulsions.

The second mechanism is the ability of corrosion inhibitors to coat and protect internal metal surfaces. However, they may also cause oil droplets to attach to solids, making the solids density comparable to that of water. This may cause particles to follow the water stream unseparated, and the oil coating appears in OiW readings. This will cause a higher oil-in-water content on the produced water process side.

This phenomenon occurred at the Buckland field on the Beryl Alpha platform. An investigation by Alfa Laval found that the high OiW content in the discharge water was due to oil-coated par ticles approximately 10 microns in size that had a density similar to water. When the injection system for corrosion inhibitor was turned off, the separation performance of the produced water treatment system was spot on track. Later, when the injection system was turn on and corrosion inhibitor dosing again reached high levels, the performance of the separator was reduced.

Heavy Oil in Produced Water
A lesser-known parameter related to produced water treatment of water streams contaminated with heavy oil is the fluid dynamic effects that appear when removing a high-density oil phase from water. In general, the removal of high-density oils from produced water is very difficult in conventional process equipment due to the small difference in densities between the oil and water. Centrifugal separators are able to take on this task as they operate with high g-forces and shor t settling distances. However, the separation of heavy oils from produced water introduces a specific flow phenomenon described as "flush through". Flush through refers to the water phase, which at certain conditions and velocities inside the disc stack, manages to expel a small por tion of the oily liquid film formed during separation into the separated water outlet; this results in poorer separation efficiency. Alfa Laval can readily model this fluid phenomenon and take it into consideration when sizing a centrifugal separation solution.

Utilities and Chemicals Consumption

What utilities and chemicals are required for centrifugal separation?
Utility consumption varies based on both the design and the size of the separator. This section provides the utility consumption for two separator designs and sizes. The first is a mediumsized separator with intermittent solids discharge and a capacity of 25 m3/h, commonly used for small-scale produced water treatment. The second is a large separator with continuous solids discharge and a capacity of up to 190 m3/h.

Weight and Footprint

What is the weight and footprint of centrifugal separators?
The weight and footprint of centrifugal separators vary depending on the model. In general, the weight and footprint are extremely small compared to conventional produced water treatment equipment. Separators have small holdup volumes in the range of 6-70 litres; the difference in weight, wet and dry, is negligible.

Is it possible to review the general arrangement of various of centrifugal separator capacities (dry and operating weight of the kit)?
General arrangement drawings detailing the package equipment, weight data and piping are available upon request. Contact your local Alfa Laval representative.

Capital Expenditures

What capital expenditures (CAPEX) are involved in purchasing centrifugal separator?
The CAPEX will vary, depending on various factors such as separator model, installation specifications, operating conditions, offshore location, requirements for regulatory compliance.

Operating Expenses

What are the operating expenses (OPEX) involved? (Utilities, chemicals, consumables/ maintenance?)
The operating expenses (OPEX) will vary, depending on the separator model. A key OPEX parameter is power consumption, which as a rule of thumb, can be set at 1 kWh/m3 of produced water processed. Some Alfa Laval separators using between 15% and 30% less power than conventional centrifugal separators. At higher flow rates, it is possible to achieve energy savings of up to 50%, in some cases.

OPEX in terms of instrument gas and water consumption has not been included in the estimates below due to differences in utilities prices. These costs are better assessed on an individual basis using utilities consumption and local gas and water prices. Chemical and heating costs also have not been included since neither chemicals nor heating are required for separator operation.

The remaining OPEX element is spare parts replacement based on standard maintenance intervals and prices. Alfa Laval offers a wide range of service alternatives - from all-inclusive performance agreements with condition monitoring to straightforward supply of spare par ts. Alfa Laval works closely with operators to establish the best maintenance programme based on their individual requirements.

Oil and gas producers often face challenges in treating produced water for discharge overboard in compliance with environmental regulations. Conventional produced water treatment technologies are complex and require pretreatment in addition the main treatment. Reject streams are often returned directly to the process, making it difficult to identify and address the issue. In addition, chemical treatments, such as corrosion inhibitors, lead to the formation and stabilization of small droplets, making it very difficult for conventional equipment to separate oil from water. What's more, the physical and chemical characteristics of the produced water vary widely and change over time within a given field. Operators of conventional technologies must then constantly adjust treatment to comply with discharge requirements.

Centrifugal separation technology provides oil and gas producers with a compact, reliable and highly efficient alternative to treat produced water under challenging conditions and, more importantly, one that can eliminate the need to recirculate hard-totreat reject streams back into process. Platform and FPSO operators seeking alternative solutions to treat produced water should consider centrifugal separation technology as a viable option.

Centrifugal separators are straightforward automated systems that separate waste oil into three phases: cleaned oil, water and solids - generally without the use of pretreatment and posttreatment stages. Used in the offshore industry for three decades, centrifugal separators are widely used in the shipping industry to treat fuel lines and handle bilge water for discharge overboard in compliance with strict environmental legislation.