apex deoiler hydrocyclone
TRANSCRIPT
Apex Process Systems 2001, 2002 Page: 1 of 9
OIL & WATER SEPARATION Using
DEOILER CYCLONES
In the
OIL & GAS INDUSTRY
Version 1.4 – Aug, 2002.
Deoiler Hydrocyclones
Apex Process Systems Pty. Ltd., 2002. Page: 2 of 9
Table of Contents
1.0 INTRODUCTION ...............................................................................................3
2.0 PRODUCT DESCRIPTION................................................................................3
3.0 OPERATING PRINCIPLES ...............................................................................3
4.0 APPLICATIONS.................................................................................................5
4.1 Oil & Gas Industry:..................................................................................5
4.1.1 Flow-Rate Control: (see Figure 2) ................................................................5
4.1.2 Oil Reject Control: (see figure 3). ....................................................................5
4.1.3 Downstream Oil-Skimmer Tank:..................................................................6
4.1.4 Pumped Deoiler Cyclone Systems:..............................................................7
5.0 BENEFITS & FEATURES..................................................................................8
6.0 CASE STUDIES ................................................................................................8
7.0 TECHNICAL INFORMATION: ...........................................................................9
Note: Cyclonixx is a Registered Trademark of Apex Process Systems Pty. Ltd.
Deoiler Hydrocyclones
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1.0 INTRODUCTION
Oil & gas production typically results in water being produced from the wells, which increases over the life of the wells. The water is separated from the Oil & Gas and environmental regulations require that the water is processed to remove residual oil, so that the water can be disposed of either back down the well, or by discharge to sea, lake or river. Deoiler Hydrocyclones are used extensively in the Oil & Gas Industry to recover the last small amounts (typically <2000 ppm) of oil from Produced Water (from the wells) or waste-water (Desalter water, process water, etc.) streams before it is discharged.
Deoiler Cyclones were developed over the past 20 years as simple and efficient Oily-Water Separators, and are typically used in all new Offshore Production Facilities, and many onshore Production Facilities and Refineries. They are compact, efficient and provide a cost-effective and sustainable method of reducing oil discharges. APS’s personnel have been involved in Deoiler Cyclone development for over 20 years, and have pioneered many improvements and innovations in this technology. APS continues to provide high levels of technical support, expertise and innovation to the Oil & Gas Industry.
2.0 PRODUCT DESCRIPTION The volumes of water produced as part of Oil & Gas production vary greatly, and can be small or large, (eg: 1,000 – 300,000 Barrels/Day; 160-48,000 m3/Day per facility). Deoiler Cyclones typically used today are quite small (eg: 40-70 mm diameter) and each Cyclone “Liner” has a relatively low capacity (250-750 Barrel/Day; 40–80 m3/Day). This may require a large number of Deoiler Cyclones or “Liners” to process the water. The Cyclone Liners are packaged inside pressure vessels, in a similar configuration to a Tube Bundle Heat Exchanger, where the number of Liners may vary from 25- 275 Liners per vessel. Typically, the pressure vessel sizes vary from 8”-42” (200-1050 mm) and are sized to suit each project’s requirements, and may include 1, 2 or more vessels. Individual vessel capacities range from ~1,000 to 80,000 BWPD for each vessel. This packaging method provides a safe, flexible, compact and inexpensive method of delivering purpose-built water treatment systems.
APS’s range of Cyclonixx Deoiler Cyclone “Liners” are manufactured from Duplex Stainless steel, with Ceramic offered for special applications. Individual Liners vary from 40– 80 mm I.D., depending on the separation performance required, although the smaller Cyclone Liners generally offer the highest oil-removal performance, and these are most commonly recommended.
APS manufactures its’ own range of high performance Cyclonixx Deoiler Cyclones, as well as manufacturing a range of retrofit Liners for many other common models
3.0 OPERATING PRINCIPLES Deoiling Cyclones are pressure-driven separators, and therefore require a pressure drop to cause separation of the oil droplets from the water stream. The Oily-Water is fed tangentially into the Deoiler Cyclone Liner, where the inlet shape forces the liquid mixture to spin in a vortex flow profile. The tapering Cyclone shape causes increased rotational acceleration as the internal diameter is reduced over the length of the liner, causing the increasing centrifugal forces to force the separation of the 2 liquids (Oil & Water). The heavier water is forced outwards toward the wall of the liner, which displaces the lighter Oil droplets toward the centre axis of the liner, where it forms a core. The heavier water flows out through the tailpipe as an underflow stream, and this is typically set at 97-98% of the inlet flow.
Deoiler Hydrocyclones
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Figure 1 - Deoiler Liner Profile.
Controlling the pressure drop (by adjusting the water outlet back-pressure) across the liner forces the lighter density oil stream to flow in the opposite direction to the main water flow, to create the “Oily core”, which is forced from the Cyclone through a centred opening near the inlet, as the “Oily Reject” stream. This is a simple and efficient separator with no moving parts. Deoiler Cyclones are designed to capture and remove relatively small oil droplets from a water stream, and they are required to do this in a single pass, and within the few seconds that it takes for the water to pass through the Cyclone Liner. Oil droplets vary greatly in size, density and surface tension, all of which affects the ability of the Deoiler Cyclone to capture and remove them. Oil removal performance is most affected by oil droplet sizes and water viscosity (eg: temperature), and these factors are generally determined by process conditions, and are not able to be changed. Consequently, the application of Deoiler Cyclones must be understood to correctly size and specify a system that has the best oil-removal performance. The chart below provides an indication of Oil Removal performance for the various sizes of Cyclone Liners
RELATIVE OIL REMOVAL for Cyclone Size
20
30
40
50
60
70
80
90
100
5 10 15 20 25 30 35Mean Oil Drop Size (Micron)
% O
il R
emov
al
40 mm50 mm70 mm
Water Outlet
Oil Reject Outlet
Oily-Water Inlet
Deoiler Hydrocyclones
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4.0 APPLICATIONS
The compact size, simplicity, ease of operation and performance of these units make them well suited for many separation tasks found in a wide range of industries, although this paper is concerned only about the Oil & Gas Industry.
4.1 Oil & Gas Industry: Deoiler Cyclones are pressure driven, and they should ideally be located as close as possible to the oily-water outlet line from the main Gravity Separator, upstream of any control valves. This will give the best separation performance as the oily water has not yet been exposed to all potential droplet shearing pressure drops across control valves, etc. It will also result in the simplest and most cost effective installation with minimum operating cost. Where adequate process is available, this pressure is used to drive the liquids through the Deoiler Cyclone unit. If there is little or no system pressure available, it is common to pump water to a Deoiler Cyclone system.
4.1.1 Flow-Rate Control: (see Figure 2) An extra advantage of Deoiling Cyclones is the simplicity of their control systems. They normally utilise the standard interface level control system of the Main Separator. Deoiler Cyclones are typically installed on the water outlet line from the Main Separator, with the Separator water interface level control valve located downstream of the Deoiler Cyclones. The flowrate through the Deoiler Cyclones will be determined by the Main Separator Interface Level Control, which will vary as the incoming water rate varies.
Separator Level Control
PRODUCTION SEPARATOR
GAS
INLET: OIL, WATER & GAS
OIL
DEOILER CYCLONE
OIL REJECT WATER OUT
WATER
LC LT
Figure 2 - Throughput Control
4.1.2 Oil Reject Control: (see figure 3). Deoiler Cyclones do not always require control of the Overflow (Oily Reject) stream, but this may be desired in order to reduce the Overflow volume. It can be achieved by installing a control valve on the Overflow line, which operates from a pressure control system that ensures a constant overflow rate, relative to pressure drop.
Deoiler Hydrocyclones
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This control system operates by taking pressure readings from the Inlet & Water Outlet lines to a Ratio Controller, which has a manually set value that is typically around 1.7 (referred to as the PDR, or Pressure Drop Ratio). The Ratio Controller seeks to maintain this PDR at the set value by controlling the backpressure on the Oil Reject line, by adjusting the Oil Reject Valve. This Ratio is determined as follows: Pinlet - Preject Pressure Drop Ratio (PDR)= Pinlet - Poutlet
where: Pinlet = Water inlet pressure Poutlet = Clean water outlet pressure Preject = Oily Reject outlet pressure
This is referred to as “Pressure Ratio Control” because it keeps a constant ratio between the two pressure drops in the Deoiler: the Inlet-Overflow, & the Inlet-Underflow pressure drop. The % overflow on Deoiler Cyclones is generally proportional to this ratio, and is generally 1.5 - 3% of the inlet flow.
Pressure Differential Ratio Control
PRODUCTION SEPAR ATO R INLET
G AS
OIL
DEOILER CYCLONE
OIL REJECT
W ATER OUT
PRESSURE RATIO CONTROL
W ATER
LC LT
PT
PT
PT
PC
Figure 3 - Pressure Ratio Control
4.1.3 Downstream Oil-Skimmer Tank: Produced water normally contains dissolved gas and may need to be routed to a Skimmer/Degasser tank prior to discharge for safety reasons. Proper design of this skimmer tank will achieve an additional amount of water polishing. A further 50-75% reduction in oil content may be possible. As the pressure drops through the Deoiler Cyclones and control valves, dissolved gas breaks out of the water. Dissolved gas flotation will occur in a vessel if designed correctly.
Deoiler Hydrocyclones
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Deoiler Cyclone & Skimmer: Series Operation
LC LC
LC
LC
DEOILER CYCLONE
3 PHASE SEPARATOR INLET
OIL OIL REJECT
DGF
GAS
RECOVERED OIL
TREATED WATER
WATER OUTLET
WATER
Signal to Pump Speed or Recycle
Figure 4 - Deoiler Cyclone & Degasser
4.1.4 Pumped Deoiler Cyclone Systems: If the existing process pressure is below 400 kPa (60 psi) it is recommended to boost the pressure by pumping the water to the Deoiler Cyclone system. It is important that guidelines are followed when designing a pumped Deoiler Cyclone system, as the pump selection and operation are critical. An incorrect pump, or even a correct pump which is operated incorrectly, can introduce considerable droplet shear, which will lead to reduced Deoiler Cyclone performance.
Pumped Cyclone system
3 PHASE SEPARATOR
DEOILER
OIL REJECT
OIL WATER
INLET
WATER OUT
GAS
LT
LC
PT
PC
Figure 5 - Pumped Deoiler Cyclone System
Deoiler Hydrocyclones
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Pump selection Low shear pumps are referred to as pumps that can be operated so that they only exert a minimal amount of shear to the pumped oily-water. Centrifugal pumps are not typically low shear pumps, but they are utilised very effectively for low-shear service. Due to their simplicity, reliability and relatively low cost, centrifugal pumps are the recommended pumps to feed Deoiler Hydrocyclone systems. For smaller or intermittently used systems, pneumatic pumps are generally more suitable. When selecting a centrifugal pump for a Deoiler Cyclone system almost any brand can be utilised as long as a number of key factors are accounted for.
Pump operation Pumps should be controlled either by a recycle loop or variable speed control. Recycle control is the simplest way of insuring that the pump is not dead-headed. The easiest method is for the pumps to take suction directly from the main Separator, with the level control valve from the source vessel located at the water discharge from the Deoiler Cyclone.
5.0 BENEFITS & FEATURES Deoiling Hydrocyclones have been installed at hundreds of different locations since their commercial development in the early 1980’s. They have been adopted as the preferred and main component of most new produced water treatment systems installed offshore Oil & Gas Industry applications during the past 10-15 years for the following reasons:
• Reliable, and consistently high oil-removal performance, • Very compact, and compared with conventional gravity separators, • Far less weight than conventional gravity or flotation separators, • A wide range of material selection options (Stainless & Duplex Steels, ceramics, etc)
for erosion and corrosion resistance, to suit each application, • No moving parts, and very low maintenance requirements, • Insensitive to motion or orientation (suited to FPSO’s and Semi-Submersibles, etc), • Modular design allowing additional units to be installed or removed (in parallel) to
handle changes in treating capacities. Units are small enough to be considered semi-portable.
• Very little instrumentation required for automatic operation of units, • Well-understood and simple technology to operate maintain, and trouble-shoot. • No special tools and little operator training required.
6.0 CASE STUDIES See the Installation List for some examples of APS supplied & installed Deoiler Hydrocyclone systems in Oil & Gas Production & Refining Operations
Deoiler Hydrocyclones
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7.0 TECHNICAL INFORMATION: Deoiler Cyclones are commonly used for the treatment of oily-water streams associated with Oil & Gas Production & Refining. A number of standard technical parameters are well established for these applications, which include materials of construction, method of packaging, process control and piping, etc. Some general information is available for some of these parameters:
7.1 Vessel General Arrangement
7.2 Typical P&ID General Arrangement