Coalescers

Paper Number 18278-MS

DOI What's this? 10.4043/18278-MS

Title: Novel Coalescer Technology in First-Stage Separator Enables One-Stage Separation and Heavy-Oil Separation

Authors: T.A. Fjeldly, E.B. Hansen, and P.J. Nilsen, Vetco Aibel

Source: Offshore Technology Conference, 1 May-4 May 2006, Houston, Texas

Language: English

Preview Abstract

Vetco Aibel (former ABB Offshore Systems) has for a long time carried out fundamental research on compact separation. A great part of the development has been to incorporate robust electrostatic coalescers into three-phase separators. The current technology enables one stage separation and accelerates separation of oil and water. The most recent product developed to enable one stage separation is the LOWACC (Low Water Content Coalescer). The LOWACC is an electrostatic coalescer element enhancing and accelerating the separation in an oil/water/gas separator. It is designed to be located downstream VIEC (Vessel Internal Electrostatic Coalescer), which is a bulk separating device, in a separator. A prototype LOWACC, together with a VIEC, has been tested on several different real crude oils ranging from API 17 to API 29. For the API 29 crude, LOWACC successfully reduced the water in oil content below 0,5% without the use of chemicals. For the challenging API 17 oil, the oil in water was reduced to below 2-5%. All the test results verified good separation even with tough separation conditions that created stable complex emulsions and small droplets. The produced water leaving the separator contained 2-200 ppm oil in water.

Introduction

The traditional oil, water and gas separation train consist of a first stage gravity separator, a second stage gravity separator and an electrostatic coalescer unit with naked electrodes. The free gas and most of the water is removed in first and second stages so that a low water content oil phase is passed on to the coalescer. A careful tuning of the water content, retention time and temperature together with de-emulsifying chemicals is necessary to obtain a satisfying separation process. For heavy oil compositions, the process becomes very difficult and oftenunstable.

By introducing an electrostatic coalescer with isolated electrodes already in the first stage separator, a much moreefficient separation process can be achieved1-3. This is demonstrated through the use of the VIEC and LOWACC described in appendix A and B. In fact, it will be shown that the traditional coalescer unit can be eliminated and that it is even possible to reduce the need for the second stage separator in many cases.

This paper describes the one stage separator design and the latest experimental results. The new data clearly demonstrate that this technology enhances heavy oil separation and improves produced water quality.

Possible applications of this technology are for oil producers on fields struggling with separation problems and to solve problems related to hydrate formation in subsea separation processes. By implementing the one stage separation, the footprint and weight of separation equipment topside will be significantly reduced. In addition, the operational expenses could be lowered as the requirement for emulsion breaker chemical is also significantly reduced. The technology can be very useful for subsea applications as itenables long tie-backs due to reduced water content in oil.

Number of Pages 6

Paper Number: 16321-MS

DOI: What's this? 10.4043/16321-MS

Title:Advanced Electrostatic Internals in the 1st Stage Separator Enhance Oil/Water Separation and Reduce Chemical Consumption on the Troll C Platform

Authors: Erik A. Wolff, ABB Offshore Systems,; Trond L. Knutsen, Norsk Hydro,; Wojciech Piasecki, ABB Corporate Research,; Peder Hansson, ABB Offshore Systems,; Pål J Nilsen,

ABB Offshore Systems

Source: Offshore Technology Conference, 3 May-6 May 2004, Houston, Texas

Language: English

Preview Abstract

The paper describes the design, testing, installation and operation of new coalescer technology in the 1st stage separator in offshore oil production. This technology is called VIEC ("Vessel Internal Electrostatic Coalescer"). The paper describes the concept as well as the technical challenges experienced. Then the results from the successful installation on Norsk Hydro's Troll C platform are presented, where large reductions in demulsifier injection have been achieved.

Introduction

The development of new coalescing devices has taken place in ABB since 1999. In 2003 the VIEC concept had passed prototype trials and was ready for field testing.

The Troll C platform was commissioned by Norsk Hydro in 1999 to exploit the thin oil layers below the Troll field gas cap (ref. 1). The Troll field shown in figure 1 is currently the largest oil producer on the Norwegian continental shelf with a daily production of over 400,000 BOPD. Oil data for the Troll field are given in Table 1.

The separation process in the 1st stage separator at Troll C was at the time not satisfactory, which gave reduced capacity and poor water level monitoring. The consequences of this challenge were a high content of water in the oil out of the 1st stage separator (above 10%), and possibility for accidental discharge to sea.

Troll Projects, managed by Mr. Trond Knutsen, is the Norsk Hydro department in charge of defining and executing modification projects on Troll B and C platforms. An internal Norsk Hydro report (ref. 2) recommended that internals should be modified and a VIEC installed. ABB received a contract in February 2003 for delivery of VIEC and adjacent replacement baffles by June 1st 2003. The project culminated with installation of the new equipment in June 2003. The results from the first half year are good and details of the project are given in this paper.

Technology description

The application of electrostatic force to help break oil/water emulsions and increase water droplet size is an old and proven technology (for example ref. 3). Oil production facilities all over the world have used electrostatic coalescers for many years to reach the sales specification on the water content of the oil. The settling velocity of water droplets in oil depends on the droplet radius squared, which illustrates the high improvement possible through increased droplet size. The traditional electrostatic coalescer is a liquid filled horizontal vessel with a residence time of 10-45 minutes, depending on the oil density and temperature. It is usually the 3rd treatment step after removal of bulk water by gravity and degassing to a suitable vapor pressure.

Coalescer Performance theory

The main feature of electrostatic coalescers is the effect of the electrostatic field strength on the conductive droplets (water) in an insulating media (oil). The water molecules in oil act as dipoles with a positive and a negative end. The electrostatic field from high voltage between two electrodes exerts a force on the droplets that press them together and helps drain the film between them. This enhances coalescence to larger droplets.

Number of Pages 7

Paper Number: 2005-159

DOI: What's this? 10.2118/2005-159

Title: Produced Fluids Separation Using A Coalescer Column

Authors: G. Renouf, L. Kurucz, D. Soveran, Saskatchewan Research Council

Source: Canadian International Petroleum Conference, Jun 7 - 9, 2005 , Calgary, Alberta

Language: English

Preview Abstract

A coalescer column - a simple, inexpensive, and environmentally friendly technology - successfully removed water from produced heavy oil emulsions. The laboratory study tested the use of the column, and the effects of column length, column packing size, temperature, flow rate, demulsifier concentration, and water addition. The use of the column improved basic sediment and water (BS&W) values after 4 hours of settling time by an average of 38%. Flowing the emulsions through the column at lower temperatures and much lower demulsifier concentrations matched the results of conventional treating. The results indicated that incorporating a coalescer column into a treatment facility allowed the reduction of demulsifier concentration from 250 ppm to 70 ppm, translating to an annual cost savings of $320,000 to $1,100,000 per battery. The column also promoted faster treating. Water droplets grew by as much as 34%, suggesting that treating time could be sped up by an average of 21% and as high as 80%.

Introduction

Heavy oil producers have reported that chemical costs represent the highest fraction of their operating expenses. A small survey of battery operators showed that demulsifier concentrations at heavy oil batteries ranged from 200 to 333 ppm (1 L/5 m3 to 1 L/3 m3) in 2001. 1 These operators also reported that demulsifier doses were rising: within the last five years, the concentration of demulsifier used to treat a typical heavy oil has risen by 25 to 50% for many reasons. A battery in the heavy oil region can easily spend over $100,000 annually on demulsifying chemicals. The two treating batteries which supplied emulsion samples for this set of experiments were estimated to spend between $400,000 and $1,100,000 every year on such costs. Heating costs are also considerable: some heavy oil batteries heat their pressurized treating vessels to 130 °C. In addition to the cost of heating, producers are becoming increasingly aware of the importance of reducing greenhouse gas production. An alternate, inexpensive, and environmentally friendly technology to help separate oil and water would be highly desirable.

One promising separation method is of the passive mechanical type: a coalescer column. Over the past 18 years, the Saskatchewan Research Council (SRC) and the University of Regina have applied this technique to break water-in-oil emulsions. 2-8 Whereas our previous work focused on resolving slop oils, this study applied the coalescer column to the treatment of wellhead emulsions.

A literature survey on the subject of coalescers and resolving crude oil emulsions is deceptive. A number of researchers use the word coalescer, but apply it to plate separators or pipes with no packing. Our use of the term restricts it to a pipe filled with some sort of porous packing material which aids in the coalescence of dispersed droplets of an emulsion. In their review of the literature on coalescing media, Stocker et al. listed the many types of packing materials that have been tested. 9 These fall into the categories of fixed media, granular packing, and fiber packing.

Number of Pages 14

File Size 292

Paper Number: 77492-MS

DOI: What's this? 10.2118/77492-MS

Title: Design of a Crude Oil Dehydration Unit

Authors: C. Noïk, J. Trapy, A. Mouret, IFP Institut Français du Petrole; G. Laborie, PROSERNAT

Source: SPE Annual Technical Conference and Exhibition, 29 September-2 October 2002, San Antonio, Texas

Language: English

Preview Abstract

The purpose of the study is to develop a compact electrocoalescer. To improve oil/water separation, definition of optimized conditions for coalescence of water droplets under an electrical field in combination with optimal hydrodynamic performances was performed. Numerical simulations carried out with the CFD code fluent permit to design a new dehydrator integrating the three functions of electrocoalescence, centrifugation and phase separation. A first part consists of two concentric cylindrical vessels used as electrodes with a tangential flow introduction. Then the speed of water droplets is accelerated in a second step by centrifugal effect. Finally, the water flow is separated from the oil phase in a third part. A laboratory prototype was built and tested in various conditions of flow rate and with different types of crude oil/water emulsions. Encouraging results led to define and patent a new concept of compact centrifugal electrocoalescer .

Introduction

As the nature of crude oil changes continuously as the producing field is depleting, the production process must be adapted to this evolution. In offshore conditions, the challenge of primary and secondary separation as well as dehydration becomes critical due to the lack of place on the platform. A compact electrocoalescer will have the advantage of being smaller and lighter than traditional ones and thus easier to install on a platform and reduce the CAPEX. Furthermore, the possibility of revamping is restricted. Moreover, it is noteworthy that the efficiency of desalting and dehydration of produced oil decreases in the presence of heavy components in oil that induce the formation of stable emulsions. Traditional application of electrostatic methods implies that the separation unit has to be sized in order to keep a satisfying efficiency during the life-time of the producing field, while emulsion breakers additives are used.

The known-effect of electrical field on water droplets is to enhance the coalescence by destabilizing by charges effects the interface of the water-in-oil emulsion phase (1). Different mechanisms are proposed depending mainly on the nature of the oil/water system and the type of electrical strength used (2). But the polar attractions between droplets are also affected by flow conditions in dehydrator unit. Most of the time shear forces or turbulence due to hydrodynamic conditions can induce droplet break-up (3,4). The final objective of water separation from oil phase is not completely reached. Coalescer design must take into account a good compromise between positive effect obtained on droplet growth by electric field and negative effect related to non-controlled hydrodynamic conditions (5).

Development of compact electrostatic coalescers appeared in the last few years (6,7,8,9). The main objective was to treat oil in smaller tank than the traditional electrocoalescer. For all systems, the first principle was to enhance coalescence by electric field using optimized pulsed D.C or A.C field. Meanwhile, taking into account the hydrodynamic conditions within the objective of water separation in the same unit, was a difficulty not overcome.

The objective of this paper is the description of the development of a compact coalescer under patenting progress (10). Firstly, numerical simulations permit to validate the concept of integrating in the same device, the three functions of electrocoalescence, centrifugation and phase separation. A prototype unit was built according to these considerations. In an experimental part, coalescence effects are enhanced by optimization of the a.c electric field strength applied. At last, complete experiment including droplet coalescence, centrifugation and phase separation are performed.

Numerical Part

Design of a new dehydrator system was intensively supported by numerical simulations carried out with the CFD code FLUENT.

Number of Pages 9

Paper Number: 77493-MS

DOI: What's this? 10.2118/77493-MS

Title: Optimization of a Horizontal Flow Electrostatic Coalescer in Offshore Gulf of Mexico Service

Authors: M.W. Heatherly, Marathon Oil Company; V.P. Buchanan, C.H. Rawlins, Kvaerner Process Systems US

Source: SPE Annual Technical Conference and Exhibition, 29 September-2 October 2002, San Antonio, Texas

Language: English

Preview Abstract

An advanced design horizontal flow oil coalescer was installed on the Marathon-operated Ewing Bank 873-A (EW- 873A) platform in early 1998. The coalescer's design has enabled it to significantly exceed design capacity while simplifying operations. Design features that aid in performance include: horizontal flow to minimize water carry-over with the bulk oil phase, a cyclonic inlet device to smooth the pipe-to-vessel transition and degas oil at inlet conditions, externally adjustable louvers to distribute oil flow evenly across the vessel, multiple externally adjustable electrostatic grids to vary field density and allow improved coalescence, and directed-flow matrix packing in the oil layer to enhance the removal of the coalesced water droplets created by the electrostatic field. Operation and maintenance improvements include: internal sampling points to quickly assess performance along the length of the coalescer, externally replaceable grid entrance bushings, and an interface draw-off line to remove chemical/solids laden pads.

This unit was installed as part of a platform upgrade and operates parallel to a vertical upflow coalescer. The existing upflow coalescer is frequently unable to achieve 1.0 % BS&W in oil effluent at lower than design rates, while the horizontal flow electrostatic coalescer consistently provides <0.4% BS&W at 120% design capacity (61,000 BOPD versus 50,000 BOPD). This paper will detail horizontal flow coalescer design, with an emphasis on internal components, and provide highlights from its four-year operating history in a side-by-side comparison to a conventional upflow coalescer.

Introduction

Upgrading and debottlenecking have become common practice for Gulf of Mexico production facilities. Marathon's EW-873A platform had an existing upflow crude dehydrator that was unable to meet the required pipeline specification at the design flow rate. Furthermore, production expansion required installation of a second unit to relieve the crude loading on the first and handle the additional oil throughput. A combined electrostatic coalescer and oil storage tank (EC/OST) design was chosen based on horizontal flow technology and containing a number of significant flow path and operating improvements. The new crude dehydrator provides high operational flexibility combined with minimum operator maintenance requirements.

Ewing Bank 873A Oil Treating

The Marathon-operated EW-873A platform began production in 1994. EW-873A now serves as a production hub for the Oyster, Arnold, Manta Ray, and Starfish subsea prospects. The platform is located in the Ewing Bank area about 130 miles south of New Orleans, Louisiana. A significant contributor to the company's deepwater portfolio, the EW-873A platform stands in 775 feet of water and has handled rates in excess of 80,000 barrels of oil per day and 70 million cubic feet of natural gas per day1.

Number of Pages 9

Paper Number: 77493-MS

DOI: What's this? 10.2118/77493-MS

Title: Optimization of a Horizontal Flow Electrostatic Coalescer in Offshore Gulf of Mexico Service

Authors: M.W. Heatherly, Marathon Oil Company; V.P. Buchanan, C.H. Rawlins, Kvaerner

Process Systems US

Source: SPE Annual Technical Conference and Exhibition, 29 September-2 October 2002, San Antonio, Texas

Language: English

Preview Abstract

Introduction

Ewing Bank 873A Oil Treating