Dec-2023

Closed-loop sampling systems can lower fugitive emission levels

Becoming a net-zero facility is easier with the right grab sampling technology. The goal of most plant operators in today’s environment is to operate net-zero facilities, but it is not an easy achievement.

Matt Dixon
Swagelok Company

Article Summary

Accidental emissions, called fugitive emissions, may happen at any location throughout refineries or chemical plants. These emissions have come under scrutiny from regulators, which adds incentives for plant operators to reduce, if not eliminate, them.

To achieve this goal, operators may need to rework the major process infrastructure significantly, but there are interim steps that can be taken to achieve more short-term goals. For example, think about how many grab sampling points exist throughout your facility. Each represents potential leak points in the system, whether it happens through spillage from sample containers or because of poorly constructed systems. Potential leaks may also arise when substandard components are used.

It is important to examine every step along the way to determine where leaks may occur, whether it is the sampling procedure, the quality of the system design, or the operator’s skill level (see Figure 1).

There are some simple, cost-effective methods for fixing leaks and reducing fugitive emissions at grab sampling locations.

Also known as closed-loop system sampling, grab sampling collects fluids in a pipeline, tank, or other industrial system and prepares them to be transferred to a laboratory for testing (see Figure 2). It is used to validate process conditions, ensure product quality, and monitor for environmental emissions. The key to grab sampling is making sure all the elements of the sampling system are working together to achieve high-quality sampling practices.

Targeting precision
Closed-loop systems provide a fresh sample that is extracted and held under the same process conditions that existed at the time of the sample. The precision of your facility’s chemical products relies on the ability to collect accurate samples. Grab sampling is one way for your plant to reduce costs and diminish product waste.

Eliminating emissions from any chemical or hydrocarbon process means preventing fluids from being released into the atmosphere. The problem can be solved with a properly designed and constructed closed-loop sampling system.

In a closed-loop system, process fluid flows through the sampling point, and some of it is collected in either a cylinder or bottle. After flowing through the sampler, the fluid flows back to the main process without exposing the operator or atmosphere to the fluid in question.

In contrast, some sampling methods may involve drawing process fluid, flowing it through a sampling point, and then eliminating the excess through flaring or another disposal process. Others may tap directly into the main process system and have operators draw fluid manually into open containers. The drawback to these methods is that they expose operators to the process fluids or expose the atmosphere through flaring or other disposal processes.

Closed-loop systems cut down on waste by returning fluid to the main process and preventing unnecessary exposure to the fluid. They are often the most effective solution to reduce fugitive emissions and keep your operators safe.

Choosing the right container
Collecting the sample itself is important, but it is even more critical to ensure the captured sample stays representative while it is being transported to the laboratory. Using an open bottle for transport, for example, may result in contamination and lead to evaporation or fractionation if proper pressure is not maintained. Typically, two different kinds of containers will be used depending on the type of system involved:
• Bottles: Bottles are often the most appropriate container to simplify sample collection and transportation. It is often recommended that bottles be used for liquids that do not require pressurisation because they can be drawn and transported without evaporation or spillage risks. To ensure tight seals, use a bottle with a self-sealing septum cap.

Another advantage bottles have is that they are a lower-cost collection option and can be replaced easily as the need arises. In addition, used bottles are easy to discard. Typically, tapered bottle shrouds keep the septum and needle aligned with the grab sampling system, which prevents accidental spillage and broken needles.
• Cylinders: It is recommended that cylinders be chosen when a gas or liquid must be captured under pressure from the sampling system (see Figure 3). Unlike bottles, cylinders keep the sample under pressure during transport which can prevent evaporation or fractionation of the chemicals.

Most sample cylinder containers are constructed using seamless tubing to ensure consistent wall thickness, size, and capacity. Internal neck smoothness prevents fluids from being trapped, enabling easy cleaning in the lab so cylinders can be reused.

Specifying a grab sampling system
For the lab analysis to be valid and useful, you must ensure your sample remains representative of the fluid within your system. In addition to maintaining the phase of a captured sample, there are several characteristics to keep in mind prior to choosing an analytical grab sampling system. Given the wide variety of configurations available, consider the following criteria:
• Pressure: Whether you are using a grab sample module or a liquid-only sampling module, the system’s maximum-rated pressure must not be exceeded
• Temperature: Each sampling module system has a maximum, and sometimes minimum, fluid operating temperature
• Hazardous material: The grab sampling system selected must protect the operator and the environment alike from the system fluid. Certain chemicals require strict leak or chemical protection
• Materials of construction: The materials used in your chosen closed-loop system must also be compatible with the system fluid
• Surface treatments: Surface treatments can reduce the absorption and adsorption of the sample fluid into metallic surfaces, leading to a more representative sample
• Purge: Some chemicals may leave residue or contaminants if not flushed from the system. Selecting a purge option provides a means to introduce a purge fluid to remove contaminants from sample lines.

Systems can also be customised to make them even safer. For example, by producing a closed-loop sampling system for specific plant applications.