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Level and Flow Solutions for Natural Gas Compression

From natural gas extraction to pipeline transmission, compressors are an essential technology employed throughout production and distribution chains to increase the pressure of natural gas by reducing its volume. At the wellhead, compression allows a low- pressure well to produce higher volumes of natural gas—in some instances, well production may be entirely dependent upon gas compression. In natural gas processing plants, intermediate and end product gases are compressed to facilitate gathering and processing operations. In pipeline transport of purified natural gas, compression stations ensure the movement of gas from the production site to the consumer. Compressors may also be used in association with above ground or underground natural gas storage facilities.

This blog post explores level and flow solutions for some common technologies used in natural gas compression. If you missed the previous posts in our series on the natural gas processing industry, you can find them here, from July 14 and July 21.

 

COMPRESSOR LUBRICATION TANK
Lubrication systems protect compressor components from increased amounts of wear and deposit formation and help the equipment run cooler and more efficiently. A wide range of engine lubricants formulated with different base oils are available. Lubricants vary by ISO grade, viscosity, flash point, and formulation. Lubricating fluids are typically stored in integral stainless steel and carbon steel tanks and in remote bulk storage tanks that are monitored for level.

Challenges: Level monitoring of lubricant reservoirs will ensure the proper functioning of compressors. Temperature shifts in integral reservoirs affect media density that will exclude some level technologies, such as pressure transmitters. Because ISO cleanliness levels increase lube change frequency, controls should be easy to remove.
Level Instrumentation:
Point Level: Echotel® Model 961 Ultrasonic Gap Switch; Thermatel® Model TD1/TD2 Switch; or Tuffy® II Float-actuated Switch
Continuous Level: Eclipse® Model 706 Guided Wave Radar Transmitter; or Jupiter® Magnetostrictive Transmitter
Visual Indication: Atlas™ or Aurora® Magnetic Level Indicators

COMPRESSOR SCRUBBER
Natural gas can travel through thousands of miles of pipeline. Compressors placed at key intervals keep the natural gas moving evenly and reliably. A typical compressor station consists of an inlet scrubber to collect liquids and slugs that may have formed in the gas pipeline. The scrubber consists of a primary section where liquids and solid parts are separated from the gas stream and a secondary section where oil mist is removed.

Challenges: The liquids collected from the suction scrubber are typically routed by way of scrubber level control valves to a low pressure (LP) tank. The vapors produced from the flashing 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 level alarms.
Level Instrumentation:
Point Level: ECHOTEL Model 961 Ultrasonic Gap Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

COMPRESSOR WASTE LIQUID
Compression station scrubbers and filters that capture liquid waste and unwanted particles route waste liquids to a storage tank. Wastes can be water condensates or heavier hydrocarbons from the natural gas. The wastes are collected in one or several tanks depending on the size of the remote station. As a waste tank fills, tank trucks are typically scheduled for tank emptying operations. As these wastes are hazardous materials, the waste holding tanks are classified as Class 1, Div. 1 areas.
underground waste tank
underground waste tank

Challenges: Measurements for both total level and interface levels between the condensed hydrocarbons and condensed water are typically made. Tank level monitoring can be provided with overflow control and alarm systems or shutdown pumps when level falls below the specified low level.
Level Instrumentation:
Point Level: ECHOTEL Model 961 Ultrasonic Gap Switch; or THERMATEL Model TD1/TD2 Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter; or JUPITER Magnetostrictive Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

FLARE KNOCK-OUT DRUM
Liquid in the vent stream can extinguish the flame or cause irregular combustion and smoking. In addition, flaring liquids can generate a spray of burning chemicals—a “rain of fire”—that create a severe safety hazard. A knockout drum collects these liquids prior to entering the flare system. A level gauge and drain connections are built into the knockout drum.

Challenges: When a large liquid storage vessel is required and the vapor flow is high, a horizontal drum is usually more economical. Vertical separators are used when there is small liquid load, limited plot space, or where ease of level control is desired. Knockout drums are equipped with instrumentation to monitor liquid level with pump out or drain facilities. High and low level alarms are frequently installed in knockout drums.
Level Instrumentation:
Point Level: ECHOTEL Model 961 Ultrasonic Gap Switch; or External Cage Float Switch
Continuous Level: ECLIPSE Model 706 Guided Wave Radar Transmitter; or E3 MODULEVEL Displacer Transmitter
Visual Indication: ATLAS or AURORA Magnetic Level Indicators

AIR AND GAS FLOW MONITORING
From the wellhead to the compression station, monitoring the flow of natural gas is essential. Other flow monitoring applications found in natural gas settings may include mass air and compressed air flow, process and waste gas flow (often required for reporting environmental emissions), and pump protection afforded by the sensing of reduced or no-flow conditions.

Challenges: Significant flow variables include pipe diameters, wide flow ranges, varying velocities, and low flow sensitivity. Flow meters ensure efficient operation at rated SCUM output and also detect leaks. A flow meter with a totalizer provides an accurate measurement of air or gas consumption. A flow switch along a pump’s discharge piping will actuate an alarm and shut down the pump when liquid flow drops below the minimum flow rate.
Level Instrumentation:
Flow Alarm: THERMATEL Model TD1/TD2 Thermal Dispersion Flow Switch
Pump Protection: THERMATEL Model TD1/TD2 Thermal Dispersion Flow Switch
Continuous Flow: THERMATEL Model TA2 Thermal Dispersion Mass Flow Meter