INDUSTRY APPLICATIONS SERIES - Interempresas

A Guide to Level Instrumentation for Onshore/Offshore Natural Gas Processing

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

2

APPLICATION PAGE

1. Inlet Separator 3

2. Chemical Injection 4

3. Amine Separation 4

4. Sulfur Treatment 5

5. Gas Dehydration 5

6. NGL Recovery 6

7. Vapor Recovery Unit 6

8. Storage Tanks 7

9. Water Processing 7

10. Compressor Lubrication 8

11. Compressor Scrubber 9

12. Compressor Waste 9

13. Flare Knock-Out Drum 10

Level & FlowApplications forNATURAL GASPROCESSING

Level and flow controlsin these applications arecrucial for both processcontrol and safetyshutdown systems.

GAS StreamLevel Applications

WATER StreamLevel Applications

Separation

Amine Separation

To Pipeline

Compression

Skim Tanksand Vessels

Sumps

Primary Water Treatment

Collection Tanks

Coalescers

8

To disposalTo reservoir

Secondary Treatment

Coalescers

Flotation Units7

�

8

Acid Gas

Sulfur Unit

Tail Gas Treatment

3

1

2

Incineration

4

5

Chemicals

6

9

Tail Gas

Offgas

Sulfur Treatment

��

�

Water

9

Liquid ProcessingNatural Gas processing is typicallyfound in crude oil drilling and process-ing operations. For information on levelapplications for crude oil processing,see our Crude Oil Processingbrochure.

Flow Applications:

Air and gas flow appli-cations are foundthroughout natural gasoperations. For a briefsummary of theseapplications, seepage 10.

� Condensate

Level Applications:

Vapor Recovery

To Fractionator

NGL Recoveryand Storage

10

NOTE: The actual nature and numberof steps in the process of creatingpipeline-quality natural gas dependsupon the source and makeup of thewellhead production stream. In somecases, several of the steps shown inthe schematic above may be integratedinto one unit or operation, performed ina different order or at alternative loca-tions, or not required at all.

�

Gas

Water Treatment

WELLHEAD

Dehydration

11

12

8

13

Good Practices:

Good practicerecommendations formajor level and flowinstrumentation can befound on page 11.

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, tur-bulent 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.

Separator

INLET SEPARATORSIN

ST

RU

ME

NT

AT

ION

1

Vertical (right): Vertical separators can accommodate large surges of liq-uids. They are well suited for high sediment loads—conical bottoms aresometimes attached for large sediment deposits. Vertical separators arepreferred when wellstreams have large liquid-to-gas ratios. These sepa-rators occupy less floor space than horizontal types and are often foundon 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

INLET STREAMIN

VERTICALHORIZONTAL

INLET STREAMIN

3

� Point Level:Series 3 Float-actuated ExternalCage Level Switch;or Thermatel® ModelTD1/TD2 Switch

� Continuous Level andInterface Level:Eclipse® Model 705;Jupiter® MagnetostrictiveLevel Transmitter; orE3 Modulevel® DisplacerTransmitter

� Visual Indication:Atlas™ or Aurora®

Magnetic LevelIndicators

Application: Chemical agents employed in natural gasprocessing include drilling fluid additives, methanol injec-tion for freeze protection, glycol injection for hydrate inhi-bition, produced water treatment chemicals, foam andcorrosion inhibitors, de-emulsifiers, desalting chemicalsand drag reduction agents. Chemicals are frequentlyadministered by way 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 INJECTIONChemical Injection Skid

2IN

ST

RU

ME

NT

AT

ION

Application: Pipeline specifications require removal of theharmful acid gases carbon dioxide (CO2) and hydrogensulfide (H2S). H2S is highly toxic and corrosive to carbonsteels. CO2 is also corrosive and reduces the BTU value ofnatural gas. Gas sweetening processes remove these acidgases and make natural gas marketable and suitable forpipeline distribution.

Challenges: Amine treatment removes acid gases throughabsorption and chemical reaction. Each of the four com-mon amines (MEA, DEA, DGA and MDEA) offer distinctadvantages in specific applications. Level control applica-tions include reactors, separators, absorbers, scrubbersand flash tanks.

AMINE SEPARATION SOUR GAS TREATMENT

INS

TR

UM

EN

TA

TIO

N

Amine Separation

3

4

� Point Level:Echotel® Model 961Ultrasonic Switch;or Thermatel ModelTD1/TD2 Switch

� Continuous Level:Eclipse Model 705Guided Wave RadarTransmitter; or JupiterMagnetostrictive LevelTransmitter

� Visual Indication:Atlas or AuroraMagnetic LevelIndicators

� Point Level:Echotel Model 961Ultrasonic Gap Switch;or Thermatel ModelTD1/TD2 Switch

� Continuous Level:Eclipse Model 705Guided Wave RadarTransmitter


Application: A sulfur recovery unit converts the hydrogensulfide in the acid gas into elemental sulfur. Of the process-es available for these conversions, the Claus process is byfar the most well-known for recovering elemental sulfur,whereas the conventional Contact Process and the WSAProcess are the most used technologies for recovering sul-furic acid. The residual gas from the Claus process is com-monly called tail gas. Tail gas is subsequently processed ina gas treating unit.

Challenges: The sulfur condenser vessel is equipped with adisengagement section on the outlet end in order to allowfor efficient separation of the liquid sulfur from the processgas. A collection vessel equipped with continuous levelcontrol is used to store and remove the sulfur product fromthe process.

SULFUR RECOVERYIN

ST

RU

ME

NT

AT

ION

Sulfur Recovery Unit

4

Application: Natural gas dehydration removes hydrateswhich can grow as crystals and plug lines and retard theflow of gaseous hydrocarbon streams. Dehydration alsoreduces corrosion, eliminates foaming, and prevents prob-lems with catalysts downstream. Compressor stations typi-cally contain some type of liquid separator to dehydrate nat-ural gas prior to compression.

Challenges: The most common dehydration method is theabsorption of water vapor in the liquid desiccant glycol. Thewithdrawal of the water rich glycol from the bottom of theabsorber is facilitated by a level control. High and low levelshut down can be applied to the reboiler, surge tank andflash separator.

GAS DEHYDRATION

INS

TR

UM

EN

TA

TIO

N

Gas Dehydration Skid

5

5

� Point Level:Echotel Model 961Ultrasonic Switch;or Thermatel ModelTD1/TD2 Switch



� Point Level:Tuffy® II Float-actuated Switch;Echotel Model 961Ultrasonic Switch;or ThermatelTD1/TD2 Switch

� Continuous Level:Eclipse Model 705Guided Wave RadarTransmitter; or JupiterMagnetostrictiveTransmitter


NGL RECOVERY & STORAGE

Application: Separating the hydrocarbons and fluids frompure natural gas produces pipeline quality dry natural gas.The two principle techniques for removing Natural GasLiquids (NGLs) are the absorption and the cryogenicexpander method. The absorption method is very similarto that of dehydration except that an absorbing oil is usedinstead of glycol. Once NGLs have been removed fromthe natural gas stream, they must be separated out, orfractionated.

Challenges: Absorption method level control is typicallyfound on flash drums, separation towers and reflux sys-tems. Cryogenic method level control is applied to theseparator and dehydrator.

INS

TR

UM

EN

TA

TIO

N

6

VAPOR RECOVERY UNIT FLASH DRUM

Application: A Vapor Recovery Unit (VRU) capturesvaluable volatile organic compounds and other richgas streams that may otherwise be a significant envi-ronmental pollutant. A Vapor Recovery Unit (VRU) col-lects from storage and loading facilities, reliquefies thevapors, and returns the liquid hydrocarbons back tostorage. Methods to recover vapors include absorption,condensation, adsorption and simple cooling.

Challenges: A VRU is a simple, economical processunit that provides EPA compliance and improves oper-ating economies by capturing up to 95% of fugitiveemissions. Critical to the VRU is the flash drum wherevapors are reliquefied. Liquid level control of the flashdrum is essential.

INS

TR

UM

EN

TA

TIO

N

Field VRU

7

NGL Recovery

6

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


� Point Level:Echotel Model 961Ultrasonic GapSwitch; orThermatel ModelTD1/TD2 Switch



� Point Level:Series 3 ExternalCage Level Switch;Tuffy II Float-actuatedSwitch; Echotel Model961 Ultrasonic Switch;or Thermatel TD1/TD2Switch

WATER PROCESSING

Application: Produced water, wash-down water or col-lected rainwater require treatment whether they’re re-used 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, coa-lescers, flotation units, and collection tanks and sumps.Interface level measurement is essential for proper drain-ing of clean water and removal of the residual oil.

INS

TR

UM

EN

TA

TIO

N

Water Wash Tank

� Point Level:Echotel Model 940/941Ultrasonic Gap Switch;Thermatel ModelTD1/TD2 Switch; orFloat or Displacer-actuated Switch

� Continuous Level:Eclipse Model705 Transmitter;or E3 ModulevelDisplacer Transmitter

STORAGE TANKSApplication: Natural gas, oil, liquid fuel, treatmentchemicals, extracted condensate from separators andwater are stored in gas fields. Unlike midstream tankfarms at terminals and refineries, field storage consistsof smaller vessels. Diesel generator fuel, potable water,and fire water are also stored in tanks.

Challenges: Tank level monitoring can be providedwith overflow control and alarm systems or shutdownpumps when level falls below the specified low level.Interface controls will sense the beginning of anoil/water interface during tank dewatering and controlthe water draw-off.

INS

TR

UM

EN

TA

TIO

N

Storage Tanks

� Point Level:Model A15 SeriesLevel Switch withoptional Proofer®;or Echotel Model961 UltrasonicGap Switch

� Continuous Level:Eclipse Model 705Transmitter; Pulsar ModelRX5 Radar Transmitter; orJupiter MagnetostrictiveTransmitter

8

9



7

NATURAL GAS COMPRESSION

Above, a gas compression skid designed for field use. The configuration of acompressor is determined by its compression capacity, by whether it is a tur-bine or reciprocating type, by its power source, and by the environmental orsound attenuation requirements that may be required.

From natural gas extraction to pipeline tranmission, compressorsare an essential technology employed throughout production anddistribution chains to increase the pressure of natural gas byreducing its volume. At the wellhead, compression allows a low-pressure well to produce higher volumes of natural gas—in someinstances, well production may be entirely dependent upon gascompression. In natural gas processing plants, intermediate andend product gases are compressed tofacilitate gathering and processingoperations. In pipeline transport ofpurified natural gas, compressionstations ensure the movement ofgas from the production site to theconsumer. Compressors may alsobe used in association with aboveground or underground natural gasstorage facilities. Three typical leveland flow applications related to gascompression follow below.

COMPRESSOR LUBRICATION TANKApplication: Lubrication systems protect compressor com-ponents from increased amounts of wear and deposit for-mation and help the equipment run cooler and more effi-ciently. A wide range of engine lubricants formulated withdifferent base oils are available. Lubricants vary by ISOgrade, viscosity, flash point, and formulation. Lubricatingfluids are typically stored in integral stainless steel and car-bon steel tanks and in remote bulk storage tanks that aremonitored for level.

Challenges: Level monitoring of lubricant reservoirs willensure the proper functioning of compressors. Temperatureshifts in integral reservoirs affect media density that willexclude some level technologies, such as pressure trans-mitters. Because ISO cleanliness levels increase lubechange frequency, controls should be easy to remove.

INS

TR

UM

EN

TA

TIO

N

Compressor Unit

10

8

� Point Level:Echotel Model 961Ultrasonic GapSwitch; ThermatelModel TD1/TD2Switch; or Tuffy IIFloat-actuatedSwitch



COMPRESSOR SCRUBBER

COMPRESSOR WASTE LIQUID

Application: Natural gas can travel through thousands ofmiles of pipeline. Compressors placed at key intervals keepthe natural gas moving evenly and reliably. A typical com-pressor station consists of an inlet scrubber to collect liq-uids and slugs that may have formed in the gas pipeline.The scrubber consists of a primary section where liquidsand solid parts are separated from the gas stream and asecondary section where oil mist is removed.

Challenges: The liquids collected from the suction scrubberare typically routed by way of scrubber level control valvesto a low pressure (LP) tank. The vapors produced from theflashing liquids are vented to the atmosphere or to a flare.The low pressure condensate is periodically trucked out.Scrubbers are often equipped with high and low levelalarms.

INS

TR

UM

EN

TA

TIO

N

11

Application: Compression stationscrubbers and filters that capture liquid waste and unwantedparticles route waste liquids to a storage tank. Wastes can bewater condensates or heavier hydrocarbons from the naturalgas. The wastes are collected in one or several tanksdepending on the size of the remote station. As a wastetank fills, tank trucks are typically scheduled for tank emp-tying operations. As these wastes are hazardous materials,the waste holding tanks are classified as Class 1, Div. 1 areas.

Challenges: Measurements for both total level and interfacelevels between the condensed hydrocarbons and condensedwater are typically made. Tank level monitoring can be provid-ed with overflow control and alarm systems or shutdownpumps when level falls below the specified low level.

INS

TR

UM

EN

TA

TIO

N

Underground Waste Tank

12

Scrubbers

� Point Level:Echotel Model 961Ultrasonic GapSwitch



9

� Point Level:Echotel Model 961Ultrasonic GapSwitch; orThermatel ModelTD1/TD2 Switch



FLARE KNOCK-OUT DRUMApplication: Liquid in the vent stream can extinguish theflame or cause irregular combustion and smoking. In addi-tion, flaring liquids can generate a spray of burning chemi-cals—a “rain of fire”—that create a severe safety hazard. Aknockout drum collects these liquids prior to entering theflare system. A level gauge and drain connections are builtinto the knockout drum.

Challenges: When a large liquid storage vessel is requiredand the vapor flow is high, a horizontal drum is usuallymore economical. Vertical separators are used when thereis small liquid load, limited plot space, or where ease oflevel control is desired. Knockout drums are equipped withinstrumentation to monitor liquid level with pump out ordrain facilities. High and low level alarms are frequentlyinstalled in knockout drums.

INS

TR

UM

EN

TA

TIO

N

Knockout Drum

13

AIR and GAS FLOW MONITORINGApplication: From the wellhead to the compression sta-tion, monitoring the flow of natural gas is essential. Otherflow monitoring applications found in natural gas settingsmay include mass air and compressed air flow, processand waste gas flow (often required for reporting environ-mental emissions), and pump protection afforded by thesensing of reduced or no-flow conditions.

Challenges: Significant flow variables include pipe diame-ters, wide flow ranges, varying velocities, and low flowsensitivity. Flow meters ensure efficient operation at ratedSCUM output and also detect leaks. A flow meter with atotalizer provides an accurate measurement of air or gasconsumption. A flow switch along a pump’s discharge pip-ing will actuate an alarm and shut down the pump whenliquid flow drops below the minimum flow rate.

INS

TR

UM

EN

TA

TIO

N

� Flow Alarm:Thermatel ModelTD1/TD2 ThermalDispersion FlowSwitch

� Continuous Flow:Thermatel Model TA2Thermal Dispersion MassFlow Meter

� Pump Protection:Thermatel Model TD1/TD2Thermal Dispersion Flow Switch

10

� Point Level:Echotel Model961 UltrasonicGap Switch; orExternal CageFloat Switch



35 diameters

5diameters

5diameters

5diameters

5diameters

5diameters

15 diameters

20 diameters

15 diameters

15 diameters

FLOW

FLOW

FLOW

FLOW

FLOW

FLOW

5diameters

50 diameters

Probe Installations

90-Degree Elbow

Two 90-Degree Elbows in Plane

Two 90-Degree Elbows out of Plane

Reduction

Expansion

Control Valve - It is recommended that controlvalves be installed downstream of the flow meter.

� Flow Meter Straight Pipe Installation, Upstream and Downstream

The figure below indicates the minimum recommended straight-run distancesrequired to obtain the desired fully developed flow profile for a Thermatel Model TA2Mass Flow Meter. If these straight-run distances are not available, the over- all accura-cy of the flow measurement will be affected; however, the repeatability of the measure-ment will be maintained. Calibration requires the TA2 sensor to be positioned in a testsection; the test section should have a sufficient upstream and downstream straightrun to ensure the formation of a fully developed flow profile. Calibration should beperformed using the same gas which the unit is calibrated for.

Good Practices for Leading Level and Flow Instrumentation

� Guided Wave Radar Probe Buildup

Natural gas, condensate and crude processing applications have some special requirements thatare not evident from Instrument Data Sheets. Experience has lead to some simple but effectiverecommendations to address these field issues not contained in Data Sheets. Natural gas, conden-sate and crude processing applications can experience paraffin, asphaltenes, grit and grimebuildup. The degree of buildup varies widely. Even in applications where it isn’t prevalent, over timeit can happen during cold weather periods or when bringing units up or down due to temperature,pressure and process material fluctuations. Like distillation columns, chambers/cages/bridles mayrequire cleaning from time to time. Even direct insertion GWR probes can at times experiencebuildup. Below are some good practices that can minimize build up and reduce maintenance time.

• Use Enlarged Coax GWR Probes with more clearance for buildup to occur.• Consider using the Model 7xG Chamber Probe whenever possible. The 7xG provides thesensitivity and performance of a coaxial probe with the viscosity immunity of a single rod.

• Insulate the probe necks of Overfill Probes to reduce any cooling at the top of the probeinside the vessel, chamber, cage or bridle.

• Chambers should be insulated even in warm weather locations. The temperaturedifferential between a warm/hot vessel (like a separator) and uninsulated chamber/cagescan be significant resulting in paraffin deposition and/or viscosity increases.

• Insulate chamber flanges to reduce any cooling at the top of the probe• Use probes with integral flushing connection to simplify flushing/dissolving puffins or grit.Flushing connections are an option available on all Magnetrol coaxial GWR probes.

• Use probes that have low end dielectric specifications (a 1.4 rating) in the application,especially for condensates.

7XDHTHPCoaxial

7XGCaged

Single Rod

7XTInterfaceCoaxial

Of relevance to:

• Gas Production• Gas Processing Facilities• Platforms• Crude Production

11

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.

CORPORATE HEADQUARTERS5300 Belmont Road • Downers Grove, Illinois 60515-4499 USA

Phone: 630-969-4000 • Fax: 630-969-9489magnetrol.com • [email protected]

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Phone: 052 45.11.11 • Fax: 052 45.09.93

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CHINA: Plant 6, No. 191, Huajin Road • Minhang District • Shanghai 201109

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ITALIA: Via Arese, 12 • 20159 Milano

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UNITED KINGDOM: Regent Business Centre • Jubilee Road • Burgess Hill, West Sussex RH15 9TL

Magnetrol & Magnetrol logotype, Atlas®, Aurora®, Echotel®, Eclipse®, Kotron®, Jupiter®, Modulevel®,

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

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

Bulletin: 41-187.0 • Effective: July 2011

AN INDUSTRY GUIDE TO LEVEL MEASUREMENT AND CONTROL FROM MAGNETROL

Other industry and special application brochures from Magnetrol include:

• Chemical• Crude Oil Processing• 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

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INDUSTRY APPLICATIONS SERIES - Interempresas