M. DIXON, Swagelok, Cleveland, Ohio
The accidental release of emissions can happen at numerous locations throughout refineries and chemical plants. Even though many of these releases are unintentional, governments around the world are implementing increasingly strict regulations. This means plant operators are required to reduce or eliminate these releases from their production processes.
This task is not easy for plant operators to achieve. In some instances, plants may need to completely rework major process infrastructure to reduce their fugitive emissions. Conversely, plant operators can take some simple proactive actions with their grab sampling systems to curb releases at these common points for fugitive emissions. For example, plants can:
A properly designed closed-loop grab sampling system is the most effective way of limiting fugitive emissions because it prevents unnecessary exposure of the process fluid to the environment. Additionally, it protects technicians from accidental exposure by keeping process fluids fully contained.
Closed-loop sampling systems: Efficient, effective and safe. Keeping fluids and gases contained within the system is the fundamental goal when it comes to reducing emissions in any chemical or hydrocarbon process. A properly designed closed-loop grab sampling system will do just that.
In a closed-loop system, process fluid is drawn and flows through the sampling point. During this time, a sample is collected in a cylinder or bottle and then the rest of the fluid is returned to the system. Since the system is a closed loop, the operator and atmosphere are never exposed to the system fluid.
This is different from other sampling methods, which may involve drawing process fluid out manually, flowing it through the sample point, and flaring or otherwise disposing of the excess. Another potential process involves having the operator tap directly into the main process tube and pour fluid into an open container.
Using a method other than closed-loop sampling introduces the possibility of unwanted emissions via flaring or exposed fluids, and exposes operators to potential safety threats. Preventing both of these potential problems is the best argument for using closed-loop grab sampling systems. In addition, a closed-loop system eliminates waste by returning the fluid to the main process rather than flaring it to the environment.
Qualities of leak-tight sampling systems. To take full advantage of closed-loop sampling systems, they must be properly designed and constructed—this design should be duplicated throughout a facility. This will ensure the systems minimize leaks at every sampling point in a plant. The following are several features to explore when choosing a closed-loop system.
Constructed from leak-tight components. Above all else, a sampling system must be constructed from the highest-quality components possible. For example, choosing low-emissions (low-E) valves that have undergone rigorous testing per American Petroleum Institute (API) standards to minimize fugitive emissions is essential to ensuring the system is as tight as possible. Certified low-E valves and other components are available throughout the industry for a variety of fluid system applications.
Designed and assembled to minimize potential leak points. Using the highest-quality components is not the only step facilities must take: even the best components can potentially leak. Another key element of creating a leak-tight, closed-loop system is to minimize the connection points in the system’s design. If leaks occur when high-quality components are used, that is usually an indication of improper installation practices. Ensure the system has been assembled and tested by well-trained technicians to help avoid these issues.
Outfitted with proper sample drawing technology. The point at which the technician draws the sample into a bottle or cylinder container represents another point where leaks can occur. Technologies are available that can help eliminate them.
In a liquid closed-loop system in which samples are collected in bottles, the fluid is commonly dispensed via a needle that pierces a rubber septum. Ideally, as the needle is withdrawn, the rubber septum reforms a complete seal. Lancet point needles are commonly used in these applications, but they may accidentally cut or core the septum, allowing fluid to escape. A better needle design option is the pencil point needle, which reduces the potential for cutting the septum with a unique design that discharges the sample through a hole on the needle’s side (FIG. 2).
In gas or volatile liquid sampling systems where cylinders are used, cylinders that feature easily operable quick connects will allow for efficient and safe connecting and disconnecting from the sampling point.
How to minimize human error. Since technicians must physically draw samples during grab sampling, it is possible that human error could be introduced into the process. Fortunately, strategies exist to limit the problems these errors may cause.
For example, using grab sampling panels with engraved placards that contain helpful details on how to operate the panel can clarify the process for technicians. Facilities can implement panels that are easier and more intuitive to operate (FIG. 3) and use available geared valve assemblies that ensure the valves required to collect samples are actuated in the proper sequence.
Finally, automating sample collections may cost more upfront, but it will ultimately reduce instances of human error. For example, automating the grab sampling panel can ensure the enclosure door is closed properly, that valves are opened correctly and in sequence, and that product and purge flow and pressures are precisely maintained (FIG. 4). While it is possible to achieve these goals when technicians are conducting the sampling, automating the process reduces the number of steps involved and will help reduce the possibility of fugitive leaks occurring.
Find the right partner. By working with the right supplier, facilities can specify easy-to-use-and-maintain grab sampling panels that come in standard, configurable designs. Using standardized panels allows facility managers to install the same system throughout the facility, which simplifies operator training, reduces the potential for errors and minimizes fugitive emissions releases in the facility.
Ultimately, grab sampling should be a process that gives facilities greater confidence that they are receiving a high-quality, up-to-spec product that can help them significantly reduce their fugitive emissions. Choosing easy-to-use, well-designed grab sampling systems and following established best practices throughout make this possible. HP
Matt Dixon is the Application Commercialization Manager for Swagelok Company.