Types of Samplers
Depending on the industrial processes being used, the type of gas or liquid sampler required can differ greatly.
From liquids to gases and from slurries to liquefied gases, it is essential that the right sampling system is chosen for the task at hand. But what are the different types to consider? Below, we present a list of some of the most common types of sampler systems that are used, offering a brief explanation of the designs and advantages that each have.
This form of sampler is used by the natural gas and specialty gas processing industries, but it also applicable in the chemical, petrochemical and refinery industries. A gas sampler directs a representative sample into a sealed cylinder rather than a bottle. This design ensures that the flow of gas is continuous, which in turn helps to ensure a more accurate sample is taken.
Pressure is a key factor, especially when dealing with volatile gases, and a properly designed cylinder is the perfect way to keep the pressure constant. Self-sealing cylinders also ensure there are no leaks, making it a safer option for operators. Cobra’s gas sampling systems are also designed to permit quick and simple disconnection, and easy sample transportation to the lab.
Liquid samplers use a fully sealed bottle or container to collect a sample. The system usually uses a multi-valve system to isolate a liquid sample and draw it via a needle into the sample container. A septum on the top of the container ensures the sample is completely sealed and cannot be contaminated.
The valve system used is very important, as it helps to ensure no disruption to the process while preventing leaks and spills, thus upholding the integrity of the sample itself. Most liquid sampling systems come with a nitrogen purge facility to ensure the integrity of each sample. Pressure can be controlled when drawing a sample via a throttle or a discharge needle, which allows gas to vent through the top of the bottle. These help prevent churning or bubbling, both of which could also compromise the sample.
It is possible to combine the design needs of a liquid sampler with those of a gas sampler, though whether this is necessary depends greatly on the process in question. Industries like the petrochemical, refinery, specialty gas and chemical commonly make use of them.
Closed Loop Samplers
Closed loop sampling is recognized as the most reliable and safest form of sampling, since the extraction is conducted with the substance completely protected from the elements. It provides emissions-free sampling, thus ensuring the release of contaminants, spills and VOCs are all avoided.
A closed loop sampling system is by far the safest option for both the environment and the operator. It is the best option for dual-phased sampling, as well as slurries, light hydrocarbons and hot oils, though it is suitable for almost every application. The alternative type of sampler design is an open sampling system, which does not draw samples directly from a processing system while it is in operation. Open sampling is done by taking the sample from storage tanks or drums at the end of the process.
In-Line Liquid Samplers
Another version of a liquid sampling system allows samples to be drawn directly from the process line rather than diverting the liquid away from direct flow of the processing system. The needle is inserted directly into a process line, drawing the sample into the container. Containment is important to ensure the sample is not contaminated, and this is accomplished through the septum at the top of the container. Flanged end connections make for simple container insertion and removal.
Liquefied Gases Samplers
The extraction of liquefied gases requires a specific design, not least because of the potential hazards that come with taking samples of the substance. The system should permit a continuous flow of the liquefied gas so as to ensure the most accurate representative sample is taken, while a fully sealed cylinder ensures the sample can neither be contaminated by outside elements, nor place the operator at risk by emitting hazardous discharge. These systems are often designed with self-sealing quick disconnect fitting, while in some designs, separate fixed expansion cylinders are used to prevent discharge to the atmosphere.
Fixed Volume Sampler
Another version of the liquid sampler, the fixed volume sampler is designed to ensure a precise sample size is drawn every time. The precision this system helps to minimize any waste from the sampling process, sometimes created by overfilling the container. These systems typically include purge capabilities to ensure the system is completely cleaned after every use, ready for another sample whenever necessary.
These samplers are available for practically all applications, whether gas, liquid or liquefied gas, in a wide variety of industries, from petrochemical and refinery to natural gas. Low-emission samplers are designed to provide greater protection for both the operator and the environment, while the minimal VOCs and no substance spillages. A key factor is a back purge, which ensures that the sampler is adequately cleaned before a new sample is sought.