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 STORAGE1IN
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CHEMICAL INJECTION2
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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 SEPARATORS3IN
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AT
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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:THERMATELModel TD1/TD2Flow Switch;CONTINUOUS:THERMATELModel TA2 MassFlow Meter
WELLSTREAMIN
4
CRUDE DEHYDRATION4IN
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RU
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CRUDE DESALTING5
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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 E3MODULEVELDisplacer Transmitter
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 Level Switch;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 DEGASSING6IN
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WATER PROCESSING7
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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 MODULEVELDisplacer Transmitter; orECLIPSE Model 705Guided W
