Adopting more renewable fuels is one of the paths to reducing carbon emissions, especially when they can be made compatible with existing distribution infrastructure. Renewable diesel is an obvious example, but there are also growing opportunities for renewable natural gas (RNG) made from a variety of sources, including agricultural wastes. Of course, digester gas from barnyard runoff is a long way from being pipeline quality natural gas. Making that conversion is the topic of my article in Pipeline & Gas Journal, Processing Raw Biogas into Renewable Natural Gas Suitable for Pipeline Blending.
Capturing biogas is not a new concept and has been used extensively by large agricultural sites as a means to deliver essentially free fuel as a byproduct of normal waste processing. But this raw biogas right out of the digester can be refined to the extent necessary for it to be used as renewable natural gas (RNG, aka biomethane in some regions) such that it can be added to pipelines interchangeably with the traditional fossil product, reducing consumption of fossil sources. Let’s take a closer look at what this requires.
Like normal natural gas, RNG is a mix of similar components, but levels can be all over the map. The main problem is its high CO2 content, which can be anywhere between 25% and 50%. Still, there are methods to reduce that level, along with various other contaminants, to make RNG indistinguishable from proper sales gas. The question becomes, what is the best technology for analyzing the composition of RNG? The first step is determining the composition of raw digester gas so the amount of refinement can be planned, and then a second check to make sure the refined gas is in spec. The best analyzer technology for this is gas chromatography.
Gas chromatography (GC) technology is firmly established as a recognized method for composition analysis of natural gas at production and custody transfer points due to its high reliability, measurement accuracy, and minimal downtime. Tens of thousands of GC analyzers are installed worldwide along natural gas pipelines, and due to the similarity of biogas measurement with natural gas measurement, GC analyzers are also trusted by biogas producers, transporters, and users.
Naturally, Emerson has an excellent GC analyzer product line. There are two models used most frequently with natural gas and biogas analysis, and custody transfer, including:
Rosemount 470XA Gas Chromatograph-The Rosemount 470XA Gas Chromatograph is also a compact, economical and reliable solution, providing accurate C6+ BTU/CV measurement. It uses the sophisticated internal sensor oven of the 770XA, and it can be installed in a wide range of environments.
Rosemount 770XA Gas Chromatograph-The Rosemount 770XA Natural Gas Chromatograph has the widest measuring and speciation range. It can measure higher hydrocarbons up to C9+, along with a more extensive list of specific sulfur compounds. This is often more than is necessary for biogas applications as it does not have the higher hydrocarbons common with fossil natural gas.
So which one is best for biogas evaluation? For dedicated biogas applications at a producer’s site, the 470XA is most popular due to its low lifetime cost. It certainly has all the required capabilities. If there are additional applications, including sophisticated analysis of natural gas, the 770XA may be necessary.
Emerson’s GC analyzer offerings are ideal for these applications, delivering accurate measurements with simple operation and low lifetime costs. Biogas producers, pipeline companies, and end users get the measurements they need without the complications, expense, and maintenance requirements of older technologies and solutions.
For more information, learn more about Emerson’s Rosemount™ Process Gas Chromatograph solutions at Emerson.com.
