I N D U S T R Y A P P L I C A T I O N S S E R I E S

A Guide to Level Instrumentation for Onshore/Offshore Oil Processing

APPLICATION PAGE

1. Production Fluid Storage 3

2. Chemical Injection 3

3. Wellstream Separator 4

4. Crude Dehydration 5

5. Crude Desalting 5

6. Crude Degassing 6

7. Water Processing 6

8. Storage Tanks 7

9. Vapor Recovery 7

Level & FlowApplications forCRUDE OILPROCESSINGLevel and flow controlsin these applications arecrucial for both processcontrol and safetyshutdown systems.

Plant Inlet

Crude StreamLevel Applications

Skim Tanksand Vessels

Sumps

Primary Water Treatment

Fluid Tanks

Desalting

Collection Tanks

Separation

Crude Dehydration

TestSeparation

3

1

2

Coalescers

Recycle Gas/Flare

Degassing

Crude Collectionand Storage Tanks

4 8

Natural Gas Processing

Natural Gas processing is found inmany crude oil drilling and processingoperations. For information on levelapplications for natural gas processing,see our Natural Gas Processingbrochure.

To disposalTo reservoir

Secondary Water Treatment

5

Coalescers

Flotation Units

Chemicals

7

Flow Applications:

6

8

Flow controls forpumps, compressors,and liquids are foundthroughout crude oilfield operations.

Water StreamLevel Applications

Level Applications:

8

7

Flow Alarm:ThermatelModel TD2ThermalDispersionFlow Switch

Continuous Gas Flow:ThermatelModel TA2ThermalDispersionMass FlowTransmitter

Vapor Recovery9

NOTE: The actual nature and number of stepsin crude oil processing most often dependsupon the source and makeup of the wellheadproduction stream. In some cases, several ofthe steps shown in the schematic below maybe integrated into one unit or operation, per-formed in a different order or at alternativelocations, or not required at all.

Natural Gas

Water

Water

2

PRODUCTION FLUID STORAGE1INSTRUMENTATION

CHEMICAL INJECTION2

INSTRUMENTATION

Application: Chemical agents employed in crude process-ing include drilling fluid additives, methanol injection forfreeze protection, glycol injection for hydrate inhibition,produced water treatment chemicals, foam and corrosioninhibitors, de-emulsifiers, desalting chemicals, and dragreduction agents. Chemicals are frequently administered byway of chemical injection skids.

Challenges: Level monitoring controls chemical inventoryand determines when the tanks require filling. The carefulselection and application of level controls to chemical injectionsystems can effectively protect against tanks running out ofchemicals or overfilling.

Chemical Injection Skid

Application: A variety of chemicals are typically stored inthe field or processing facility to expedite processing timeby preconditioning an inlet fluid. These fluids may first enterinto a hold tank to allow upstream solids and liquids time toseparate prior to production, which allows the facility tobetter handle upset conditions without stopping production.Stored additive chemicals include dispersants, flocculants,surfactants, glycols, diluents and rust inhibitors.

Challenges: Fluids are typically stored in a series of out-door steel tanks. The tank fluid volume should be continu-ously monitored since level variations may lead to upsets.Tanks contain agitated media with suspended solids thatcan coat floats, displacers and probes.

Continuous Leveland Interface Level:Eclipse Model 705 GWRTransmitter with EnlargedCoaxial Probe; or Pulsar

or R82 Non-contacting,Pulse Burst RadarTransmitters

Point Level:Echotel Model 961Ultrasonic Switch;Thermatel ModelTD1/TD2 Switch;Tuffy II Float-actuated Switch

Continuous Level:Eclipse Model 705Guided Wave RadarTransmitter; or Jupiter

MagnetostrictiveLevel Transmitter

Visual Indication:Atlas or Aurora

Magnetic LevelIndicators can besupplied withswitches ortransmitters

Storage Tanks

3

Point Level:Thermatel Model TD1/TD2Thermal Dispersion Switch;or Model A15 SeriesDisplacer-ActuatedLevel Switch

WELLSTREAM SEPARATORS3INSTRUMENTATION

Application: Separators are large drums designed toseparate wellstreams into their individual components.They are commonly designed to separate two-phase(gas/liquid) or three-phase (gas/crude/water) wellstreams.Separators are also classified according to horizontal orvertical configuration (see below), operating pressure,turbulent or laminar flow, and test or production separation.

Challenges: Interface level measurement will actuate avalve to adjust vessel level. An emulsion layer along theoil/water interface can contaminate the oil with water orthe water with oil. Foaming along the gas/liquid interface,if entrained, can cause liquid carryover or gas blowby.

Oil Field Separator

Point Level:Series 3 Float-actuatedExternal Cage LevelSwitch; ThermatelModel TD1/TD2Switch; Model A15Series Displacer-Actuated Level Switch

Continuous Leveland Interface Level:Eclipse Model 705;Jupiter Magneto-strictive LevelTransmitter;or E3 Modulevel

Displacer Transmitter

Visual Indication:Atlas or AuroraMagnetic LevelIndicators canbe supplied withswitches ortransmitters

Vertical (right): Vertical separators can accommodate large surges ofliquids. They are well suited for high sediment loads; conical bottoms aresometimes attached for large volumes of sediment. Vertical separatorsare preferred when wellstreams have large liquid-to-gas ratios. Theseseparators occupy less floor space than horizontal types and are oftenfound on offshore platforms where floor space is at a premium.

Horizontal (below): These separators are well suited for three-phaseseparation because of their large interfacial area between the two liquidphases. Horizontal types are preferred when wellstreams have high gas-to-oil ratios, when wellstream flow is more or less constant, and whenliquid surges are insignificant. These separators also have a muchgreater gas/liquid interface area, which aids in the release of solution gasand in the reduction of foaming.

TWO PRINCIPAL TYPES OF SEPARATORS

NATURAL GAS

WATER

GAS OUT

OIL OUTWATER OUT

OILEMULSION

GAS OUT

OIL OUT

NATURAL GAS

WATER

WATEROUT

OIL

EMULSION

WELLSTREAMIN

VERTICALHORIZONTAL

Flow Indication:ALARM:Thermatel ModelTD1/TD2 FlowSwitch;CONTINUOUS:Thermatel ModelTA2 Mass FlowMeter

WELLSTREAMIN

4

CRUDE DEHYDRATION4INSTRUMENTATION

CRUDE DESALTING5

INSTRUMENTATION

Application: Not all water is removed from crude oil duringthe first stage of gravity separation. Separated crude maycontain up to 15% water which exists in an emulsified formthat is difficult for a separator to remove. The oil and wateremulsion must be broken down so that the water can beremoved before the crude is shipped. De-emulsificationprocesses are accomplished using chemical agents suchas glycol and heat.

Challenges: Level control is found on two-phase andthree-phase water knockout drums, heater treaters andchemelectric dehydrators. Interface measurement is criticalin dehydration as it keeps the water-emulsified oil fromflowing over the separator weir.

Knock-out Drum

Point Level:Series 3 Float-Actuated ExternalCage LevelSwitch

Continuous Leveland Interface Level:Eclipse Model 705Guided Wave RadarTransmitter; or E3Modulevel DisplacerTransmitter

Visual Indication:Atlas or AuroraMagnetic LevelIndicators can besupplied with switchesor transmitters

Application: Salt in the crude stream presents serious cor-rosion and scaling problems, and must be removed. Salt isdissolved within the remnant brine of the crude oil.Desalting removes both salt and the residual free water.Field desalting is necessary due to pipeline requirements.

Challenges: Level instrumentation is integral to single andtwo-stage desalting systems, multiple orifice plate mixers,and the settler tank of a chemical desalter. Interface levelcontrol keeps free water from hitting the desalter electrodesand prevents expensive damage. The interface level shouldbe kept constant, otherwise electrical field changes will dis-turb electrical coalescence.

Two-stage Desalter

Point Level:Series 3 Float-actuated ExternalCage LevelSwitch; ThermatelModel TD1/TD2Level Switch

Continuous Level:Eclipse Model 705Transmitter withEnlarged Coaxial probe;or E3 ModulevelDisplacer Transmitter

Visual Indication:Atlas or AuroraMagnetic LevelIndicators can besupplied with switchesor transmitters

5

CRUDE DEGASSING6INSTRUMENTATION

WATER PROCESSING7

INSTRUMENTATION

Application: By removing dissolved gases and hydrogensulfide, crude stabilization and sweetening processesdiminish safety and corrosion problems. Gases areremoved by a stabilizer. Sweetening employs stabilizationor vaporization processes along with a gas or steam-basedstripping agent.

Challenges: Removing dissolved gases by stabilizationrequires level control in the reboiler unit. Sweetening bystage vaporization and trayed stabilization require levelcontrol in a series of staged separators. Sweetening byreboiled trayed stabilization requires additional level controlin a reboiler.

Reboiler

Continuous Level:E3 Modulevel DisplacerTransmitter; or EclipseModel 705 GuidedWave Radar Transmitter

Visual Indication:Atlas or Aurora MLIscan be supplied withswitches or transmitters

Point Level:Series 3 Float-Actuated ExternalCage Level Switch;or Tuffy II Float-actuated Switch

Application: Produced water, wash-down water orcollected rainwater require treatment whether theyrereused for reservoir flooding or simply disposed of. Watercollected from process operations contains hydrocarbonconcentrations too high for safe discharge. Suspendedhydrocarbon droplets in water also hinders well-injection.

Challenges: Treatment equipment is similar to three-phase separators except that water is the main product.Level control is found on skim tanks, precipitators,coalescers, flotation units, and collection tanks andsumps. Interface level measurement is essential for properdraining of clean water and removal of the residual oil.

Water Wash Tank

Point Level:Echotel Model961 UltrasonicGap Switch;Series 3 Float-ActuatedExternal CageLevel Switch

Continuous Level:Eclipse Model 705;or Kotron Model 805Smart RF Transmitter;or E3 ModulevelDisplacer Transmitter

Visual Indication:Atlas Magnetic LevelIndicator can besupplied with switchesor transmitters

6

PROCESS & STORAGE TANKS8INSTRUMENTATION

VAPOR RECOVERY UNIT FLASH DRUM9

INSTRUMENTATION

Application: Crude oil and water are stored in oil fields.Unlike midstream tank farms at terminals and refineries,field storage consists of smaller vessels associated with oiland water processing. Diesel generator fuel, potable water,and fire water are also stored.

Challenges: Tank level monitoring can be provided withoverflow control and alarm systems or shutdown pumpswhen level falls below the specified low level. Interface con-trols will sense the beginning of an oil/water interface duringtank dewatering and control the water draw-off.

API 2350: New recommended practices regarding tank overfillprotection for above-ground storage tanks that receive Class I(flammable) liquids outline that careful selection and applicationof level controls can effectively protect against tank overfills.

Storage Tanks

Point Level:Model A15 SeriesLevel Switch withoptional Proof-er

Ground Check; orTuffy II Float-Actuated Switch

Continuous Level:Eclipse Model 705 Transmitterwith Flexible Probe; PulsarModel RX5 Non-Contacting,Pulse Burst Radar Transmitters;or E3 Modulevel DisplacerLevel Transmitter

Application: If allowed to escape into the atmosphere,hydrocarbon vapors diminish income through loss of hydro-carbon volume and create fire hazards and pollution prob-lems. A Vapor Recovery Unit (VRU) collects vapors fromstorage and loading facilities, reliquefies the vapors andreturns the liquid hydrocarbons back to storage.Methods to recover vapors include absorption, condensa-tion, adsorption and simple cooling.

Challenges: A VRU is a simple, economical process unitthat provides EPA compliance and improves operatingeconomies by capturing up to 95% of fugitive emissions.Critical to the VRU is the flash drum where vapors are reliq-uefied. Liquid level control of the flash drum is essential.

Field VRU

Continuous Level:EclipseModel 705Guided Wave RadarTransmitter;E3 ModulevelDisplacerTransmitter

Visual Indication:Atlas or AuroraMagnetic LevelIndicators can besupplied withswitches ortransmitters

Point Level:Series 3 Float-Actuated ExternalCage Level Switch;or Tuffy II Float-actuated Switch; orEchotel 961 Switch

Flow Indication:CONTINUOUS:ThermatelModel TA2Mass Flow Meter

7

Chemical Flue Gas Desulfurization Food & Beverage Interface Level Measurement Life Science Mass Flow Measurement Nuclear Power Petroleum Refining

Power Generation Pulp & Paper Mills Renewable Energy Steam Generation Tank Bridle Level Measurement Understanding Safety Integrity Level (SIL) Water & Wastewater

AN INDUSTRY GUIDE TO LEVEL MEASUREMENT AND CONTROL FROM MAGNETROL

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Proof-er, Pulsar, Thermatel and Tuffy, are registered trademarks of Magnetrol International.

Copyright 2011 Magnetrol International. All rights reserved. Printed in the USA.

Bulletin: 41-186.0 Effective: April 2011

PLEASE NOTE: The instruments recommended in these brochures are based on field experience with similar applications andare included as a general guide to level and flow control selection. Because all applications differ, however, customers shoulddetermine suitability for their own purposes.