Level Control Solutions for Natural Gas Applications

The efficiency and safety of natural gas processing applications is dependent on accurate level measurement. With good level control solutions, natural gas processes such as separation, chemical injection and gas dehydration can run smoothly. This blog post discusses level instrumentation for use in natural gas processing applications.

INLET SEPARATORS
natural_gas_applications_1Separators are large drums designed to separate 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 or vertical configuration (see below), operating pressure, turbulent or laminar flow, and test or production separation.
Challenges: Interface level measurement will actuate a valve to adjust vessel level. An emulsion layer along the oil/water interface can contaminate the oil with water or the water with oil. Foaming along the gas/liquid interface, if entrained, can cause liquid carryover or gas blowby.
Two Principal Types of Separators
Vertical: Vertical separators can accommodate large surges of liquids. They are wellnatural_gas_applications_2 suited for high sediment loads—conical bottoms are sometimes attached for large sediment deposits. Vertical separators are preferred when wellstreams have large liquid-to-gas ratios. These separators occupy less floor space than horizontal types and are often found on offshore platforms where floor space is at a premium.
Horizontal: These separators are well-suited for three-phase separation because of their large interfacial area between the two liquid phases. Horizontal types are preferred when wellstreams have high gas-to-oil ratios, when wellstream flow is more or less constant, and when liquid surges are insignificant. These separators also have a much greater gas/liquid interface area, which aids in the release of solution gas and in the reduction of foaming.natural_gas_application_3
Level Instrumentation:
Point Level: Series 3 Float-actuated External Cage Level Switch; or Thermatel® Model TD1/TD2 Thermal Dispersion Switch
Continuous Level and Interface Level: Eclipse® Model 706 Guided Wave Radar Transmitter; Jupiter® Magnetostrictive Level Transmitter; or E3 Modulevel® Displacer Transmitter
Visual Indication: Atlas™ or Aurora® Magnetic Level Indicators

CHEMICAL INJECTION
Chemical agents employed in natural gas processing include drilling fluid additives, methanol injection for freeze protection, glycol injection for hydrate inhibition, produced water treatment chemicals, foam and corrosion inhibitors, de-emulsifiers, desalting chemicals and drag reduction agents. Chemicals are frequently administered by way of natural_gas_applications_4chemical injection skids.
Challenges: Level monitoring controls chemical inventory and determines when the tanks require filling. The careful selection and application of level controls to chemical injection systems can effectively protect against tanks running out of chemicals or overfilling.
Level Instrumentation:
Point Level:
Echotel® Model 961 Ultrasonic Gap Switch; or THERMATEL Model TD1/TD2 Thermal Dispersion Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter; or JUPITER Magnetostrictive Level Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

AMINE SEPARATION SOUR GAS TREATMENT
Pipeline specifications require removal of the harmful acid gases carbon dioxide (CO2) and hydrogen sulfide (H2S). H2S is highly toxic and corrosive to carbon steels. CO2 is also natural_gas_applications_5corrosive and reduces the BTU value of natural gas. Gas sweetening processes remove these acid gases and make natural gas marketable and suitable for pipeline distribution.
Challenges: Amine treatment removes acid gases through absorption and chemical reaction. Each of the four common amines (MEA, DEA, DGA and MDEA) offer distinct advantages in specific applications. Level control applications include reactors, separators, absorbers, scrubbers and flash tanks.
Level Instrumentation:
Point Level:
ECHOTEL Model 961 Ultrasonic Gap Switch; or THERMATEL Model TD1/TD2 Thermal Dispersion Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

SULFUR RECOVERY
natural_gas_applications_6A sulfur recovery unit converts the hydrogen sulfide in the acid gas into elemental sulfur. Of the processes available for these conversions, the Claus process is by far the most well-known for recovering elemental sulfur, whereas the conventional Contact Process and the WSA Process are the most used technologies for recovering sulfuric acid. The residual gas from the Claus process is commonly called tail gas. Tail gas is subsequently processed in a gas treating unit.
Challenges: The sulfur condenser vessel is equipped with a disengagement section on the outlet end in order to allow for efficient separation of the liquid sulfur from the process gas. A collection vessel equipped with continuous level control is used to store and remove the sulfur product from the process.
Level Instrumentation:
Point Level:
ECHOTEL Model 961 Ultrasonic Gap Switch; or THERMATEL Model TD1/TD2 Thermal Dispersion Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

GAS DEHYDRATION
Natural gas dehydration removes hydrates which can grow as crystals and plug lines and retard the flow of gaseous hydrocarbon streams. Dehydration also reduces corrosion, eliminates foaming, and prevents problems with catalysts downstream. Compressor stations typically contain some type of liquid separator to dehydrate natural gas prior to natural_gas_applications_7compression.
Challenges: The most common dehydration method is the absorption of water vapor in the liquid desiccant glycol. The withdrawal of the water rich glycol from the bottom of the absorber is facilitated by a level control. High and low level shut down can be applied to the reboiler, surge tank and flash separator.
Level Instrumentation:
Point Level:
Tuffy® II Float-actuated Switch; ECHOTEL Model 961 Ultrasonic Gap Switch; or THERMATEL TD1/TD2 Thermal Dispersion Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter; or JUPITER Magnetostrictive Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

Natural Gas Processing

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