The Monitor

Production Process Insights

How To Safely Sample Liquefied Petroleum Gas (LPG)

Posted by Jeff McKinney on 3/29/16 8:00 AM
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A range of petrochemical liquids and gases are stored and transported under high pressure, including liquefied petroleum gas (LPG). LPG is a two-phase liquid – a gas that is pressurized, stored and transported in its liquid phase, with high vapor pressures. Operators and the environment both face risks if unsafe LPG sampling solutions are employed.

Because of the often high pressures of petrochemical processes, any petrochemical industrial sampling processes, including that of LPG, places a high importance on protecting operators. Safe, representative sampling solutions include low-emission (low-e) sampling solutions, which allow for sampling to be done without operator exposure to harmful vapors. Low-e samplers are designed to provide the greatest amount of protection for both operators and the environment, with no spillage and minimal release of volatile organic compounds (VOCs) – chemicals that form vapor at even room temperature.

The best low-e sampling solutions feature tubing, fittings and sample cylinders made from materials that are non-reactive to the product being sampled. Sampling points never should be placed where expected operating pressures exceed the recommended pressure ratings of sampling equipment, and the line must not exceed the pressure ratings for the sample panel.

Safe petrochemical sampling

For sampling of LPG, connections to the product line include one to release the sample, one to return the sample in the vent, and one to collect and safely process off gases or vapors released during the sampling process to eliminate product release to the local environment and operators.

For example, the Sentry® MLG low-emission sampler incorporates several features to provide for safe, simple and representative sampling. A six-port tandem valve simplifies sampling by replacing multiple valve operations with just one ergonomically-designed sampler. The sampler action is repeatable, so the sample is always as representative as possible. By using an expansion vessel to reduce sample cylinder volume after the sample is captured, both safety (outage space for transport of the cylinder assembly) and representative sampling are assured for the most accurate data analysis results.

Safe sampling of LPG also requires using a stainless steel sample cylinder for collection and transport of the sample. Generally, this is a stainless-steel pressure-rated cylinder with inlet and outlet isolation valves to contain the sample within the cylinder, and connections to easily remove the cylinder assembly from the sample panel. These types of sample cylinder assemblies allow for samples to be collected at the pressure of the process fluid or gas, assuring that the sample constituents that can change state with pressure reduction are not lost during sample collection. Sample cylinder assemblies need to be transported for analysis to ensure process production output is stable, efficient and safe. Sentry sample cylinder assemblies provide a safe method of transport in addition to collection.

To eliminate cross-contamination between samples so that samples are truly representative, an optional purge system using an inert gas (N2) can be added. This purge system is used to clear the sample lines of product when application requirements specify the need.

Sentry low-e sampling solutions are suitable for sampling LPG and other petrochemical gases and liquids within processes of any pressure, including high pressures. These samplers ensure representative samples and operator and environmental safety, every time.

Learn more about our sampling solutions for the petrochemical industry here.

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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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