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The Fluid Systems Engineering and Management Blog

by Swagelok Northern California

Choosing an Industrial Gas Sampling Point in Legacy Refineries

by Morgan Zealear, on 11/18/21 9:00 AM

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Legacy industrial refineries often undergo retrofitting to improve efficiency and safety. An area to consider retrofitting that improves both efficiency and safety is an upgrade in gas sampling. Gas sampling indicates the composition of chemicals in processing which may point to issues that are related to production efficiencies such as leaks, unintended side-reactions, and contaminants entering the system. Identifying and correcting these issues also improves safety for operators as they may prevent damage to components that lead to leaks and exposure to chemicals.

While this is an important process for meeting safety and production standards, there are several issues that can occur while gas sampling. These issues may make sample data inaccurate or may not provide a whole picture of what is occurring during processing.

This article will discuss the challenges that may arise during gas sampling with a specific focus on the sampling points and reasons for sampling variability. 

Difficulties in Gas Sampling for Legacy Refineries

Gas sampling plays an important role for the continued efficient operation of a refinery. However, gas sampling may be problematic if sample variability does not provide the whole picture of the composition of the gas. There are several reasons for this variability in sampling.

Sample Point Variability

Perhaps the most significant problem with getting an accurate analysis of a gas is sample point variability. Samples can be collected at the well head, separator outlet, stock tank, and pipeline terminal, and at several locations from the terminal to the refinery gate.

It is recommended to sample along many points of the refinery process. Crude oils undergo changes in properties as they progress along the supply chain. At any of these points, an unintended side reaction or change could occur.

Legacy refineries may have issues with sampling in many of these locations due to existing infrastructure limiting space for sampling systems. In addition, these locations may experience differences in ambient temperatures and pressures, which may cause inaccurate sampling.

The Influence of Variable Operating Conditions on Sample Point Variability

Variations in temperature and pressure may result in differences in sampling as certain molecules of the gas mixture may respond differently to these conditions. During condensation, for example, a molecule’s response to these conditions may result in more or less of that molecule reaching the sensor (for active or passive sampling) or gas collection chamber (in the case of grab sampling), causing the sample to inaccurately indicate the gas composition. In addition, the time of the sampling may incur a different result in sampling as the upstream processes from the sampling location may be undergoing different processing.

Legacy refineries—with a conglomerate of components from past updates and retrofitting—may experience more of these issues as the sensor locations in the processing system may be limited based on existing infrastructure rather than where they obtain the most accurate sample.

These refineries can update existing equipment and utilize sampling strategies to get a more accurate sample, monitor gas, prevent leaks, and keep operators safe.

Updating Legacy Refinery Components for Gas Sampling

Several components used for gas sampling can be updated in a legacy refinery to help improve sampling accuracy. These components are dependent on the type of sampling utilized and the existing infrastructure.

Type of Gas Sampling Implemented

The type of gas sampling used—active, passive, or grab sampling—is determined based on how different molecules react to changes in pressure and temperature. An active sampling method that utilizes pumps to make sure all molecules of the gas are sampled might be preferred over a passive sampling method that analyzes the composition of gases as they pass over a sensor (with gas density potentially causing issues for which gas contacts the sensor). Because grab sampling only gives a snapshot of the gas sampled at that specific time, it should be performed at regular intervals to account for the variation in downstream processing.  

Existing Infrastructure

The existing infrastructure—such as limited space—may also influence the type of sampling used and the locations throughout processing which would work for gas sampling in legacy refineries. In addition, gas sampling could be utilized around areas of concern (e.g. areas with the biggest risks of leakage) to add an additional layer of protection in case problems occur.

Ancillary Components for Gas Sampling

The components needed for gas sampling are directly related to the type of gas sampling used which is related to the point location and limitations of existing infrastructure. The type of gas sampling used would determine if pumps, sensors, or collection cylinders are needed for gas sampling and analysis. In addition, the gas composition would influence the tubing and material characteristics for these components.

An expert can help with retrofitting a legacy refinery to determine gas sampling methods and gas sampling needs.

Expert Consultation to Help You Choose an Industrial Gas Sampling Point

Accurately sampling gases is critical for determining if refineries are operating at peak efficiency. By consulting with an expert, your specific gas sampling needs can be determined based on existing conditions and infrastructure.

Swagelok has experts that can examine a retrofitted refinery’s blueprints to determine the optimal point locations for gas sampling. They will also be able to suggest the necessary upgrades to components for sampling to provide accurate data on gas composition.

Swagelok Northern California has worked extensively with local refineries to achieve reliable and consistent sampling. Our Field Engineers have extensive knowledge of gas sampling applications in refineries and can provide onsite consultations to determine the ideal gas sampling point for your legacy refinery.

To learn more about how Swagelok Northern California can help you with your gas sampling needs, contact our team today by calling 510-933-6200.


Morgan Zealear-1Morgan Zealear | Product Engineer – Assembly Services

Morgan holds a B.S. in Mechanical Engineering from the University of California at Santa Barbara. He is certified in Section IX, Grab Sample Panel Configuration, and Mechanical Efficiency Program Specification (API 682). He is also well-versed in B31.3 Process Piping Code. Before joining Swagelok Northern California, he was a Manufacturing Engineer at Sierra Instruments, primarily focused on capillary thermal meters for the semiconductor industry (ASML).

Topics:Gas SystemsAssembly ServicesMission Critical

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