RNG is purified biogas suitable for injection into a natural gas pipeline.
The organically sourced biogas is processed to remove non-energy yielding components such as water, CO2, nitrogen and other contaminates like H2S. Biogas is produced from various biomass sources through biochemical processes, including anaerobic digestion. RNG can be used as a fuel for transportation, electricity generation or heating. RNG is a carbon-neutral, or negative, fuel and by capturing atmospheric methane it significantly reduces otherwise GHG emissions.
Most of the completed RNG projects in the U.S. were developed near natural gas pipelines for easy access to market. The systems resembled any small gas producer with gas production and processing onsite. Injection of the gas into the grid is controlled by a logic system connected to a control valve after determination of the gas’ composition through proper sample conditioning and analysis. Many newer RNG projects are not located near natural gas pipelines. In these cases, the gas must by transported in high pressure vessels by trucks to a pipeline interconnect. This process is called "a virtual pipeline."
Pipeline-ready biogas must be scrubbed of all contaminants to meet tariff limits. The raw gas is removed from its source and "sweetened" to remove dangerous H2S. The gas is then pressurized and dehydrated to remove water then upgraded by reducing the CO2 and nitrogen levels. The methane level of the RNG after cleaning and upgrading exceeds 95%. The main instruments used to determine commercial suitability are a gas chromatograph and moisture analyzer. In virtual pipeline applications, the gas is compressed to about 4,000 psi, loaded into canisters and carried to the end user where it is decompressed for use.
Algas-SDI TRUXX: Making gas accessible, easy to use
The Algas-SDI TRUXX decompression equipment heats the compressed RNG and injects it into the transmission line or distribution system. The TRUXX system heats the gas via a dry electric or gas fired waterbath heater to counteract the refrigeration effect caused by the expansion of the gas — which is known as the Joule-Thomson effect. The TRUXX system also incorporates a Mustang Sampling instrumentation package and custody transfer flow meter. Because the TRUXX system packages the heater, meter and the Mustang Sampling instrumentation kit into one 20-foot container, customers can begin to flow gas a mere six hours after receiving the equipment on site. Multiple TRUXX decompression systems can be installed at an interconnect site, allowing the developer to utilize RNG from many different sources.
Some interconnect sites operate at relatively high pressures. To "drain" the compressed RNG trailer as much as possible, the Algas-SDI central control system incorporates a booster compressor. Once the pressure in the trailer falls below the pipeline pressure, the control system diverts the gas to a booster compressor which elevates the gas pressure to allow injection into the pipeline. Algas-SDI’s control system also modulates the amount of gas injected into the pipeline from each TRUXX unit, which minimizes the amount of time for a trailer to decant.
Gas measurement and control are accomplished by utilizing an Analytically Accurate® System integration within the Algas-SDI skid. Mustang Sampling products determine the efficacy of the RNG and report and record any contaminants present. Each source of compressed RNG runs through a Pony® Probe Enclosure and is transferred using Mustang’s Heat Trace Tube Bundle to a Mustang® Modular Analyzer Distribution Panel. This distributes the conditioned gas samples to a Mustang® Moisture Analyzer System and Rosemont® 370 XA GC. The separate samples ensure compliance with the health-protective standards. Only after the gas quality passes all local tariffs and requirements can it be injected into the natural gas pipeline grid.
Mustang Sampling is the innovator of Analytically Accurate® solutions within sample conditioning systems. It provides custom solutions of products and services globally to the natural gas, NGL, renewable natural gas and LNG industries — including hydrogen blending and carbon sequestration.
For more information, visit mustangsampling.com or call (713) 482-6930.
