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Production Process Insights

How to Sample Cryogenic Liquids Safely

Posted by Jeff McKinney on 5/4/16 8:23 AM
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how to sample cryogenic liquids safely

In the petrochemical industry, it often is necessary to ship and store product that would be gaseous at ambient conditions – such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG) – as liquid. The product is stored or transported cold to minimize its volume.

Increasing Popularity of LNG

For instance, LPG is comprised chiefly of propane or butane, and is a byproduct of gasoline and diesel fuel refining. It remains a liquid under low pressure and can be stored and transferred in appropriate vessels. LNG is a natural product occurring in underground deposits and is more than 90 percent methane (CH4).

Natural gas retains its gaseous form down to a temperature of -161°C. Below this point, it becomes a liquid and occupies a far smaller volume. LNG is about 1/600th the volume of natural gas at standard temperature and pressure. When LNG is cooled to -161°C (-259°F), it becomes a clear, colorless, odorless liquid, weighing less than half the weight of water – and will float when spilled on water.

LNG terminals have been appearing rapidly along the U.S. Gulf coast and elsewhere, because the low price and high supply of U.S. shale gas has created an export market. One example: INEOS, an industry innovator, just shipped the first liquefied ethane on special ships from Marcus Hook, Penn., to Europe for use as an alternate feedstock.

Due to the increasing popularity of LNG, many petrochemical sampling systems include at least one cryogenic application.

How LNG and LPG Become Liquid

A spiral heat exchanger is the core equipment in large baseload LNG and LPG plants applying mixed refrigerant cycles for natural gas cooling and liquefaction. The heat exchanger and other equipment is installed in a coldbox to treat and liquefy cryogenic liquids and gases.

Within this process, for custody transfer purposes, the cryogenic LPG and LNG must be sampled to ensure the end customer receives pure product unadulterated by excess water vapor or nitrogen. This requires a sampler that can handle the extreme cold temperatures necessary for the process.

Cryogenic Low-Emission Sampling

To meet the demands of this application, cryogenic sampling solutions require specially designed and engineered sampling valves and quick disconnect fittings rated for the cold temperatures – design specifications of -320°F are common. Due to seal issues, tandem valves are not appropriate for use in these applications.

Sentry® low-emission (low-e) samplers such as the MCL sampler often are customized with special elastomers for cryogenic petrochemical gas or liquid applications. Low-e sampling is the best solution for petrochemical processing due to the often high pressures and dangerous chemical nature of the processes. Low-e sampling systems are safe, simple to use, yield representative samples for accurate analysis, and comply with stringent requirements for operator and environmental safety.

Whether you are sampling liquid or gas, our petrochemical sampling solutions can meet your application needs at any temperature extreme.

Sentry's Industrial Representative Sampling eBook

Topics: Hydrocarbon Processing

Written by Jeff McKinney

As an industry manager for chemical and petrochemical refining, Jeff is an expert in those markets and is experienced in power generation as well. Jeff is focused on serving these key markets and sharing information on how Sentry sampling and monitoring products and systems can meet any petrochemical or chemical application, anywhere. He is responsible for our market strategy and product offerings, and is always interested in exchanging information on specific industry applications and solutions that meet customer needs.

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