Engineering Renewable Natural Gas Solutions

Emerson pressure management business development manager Isaac Droessler, and pressure management director, Arrchana Lakshmanan, recently published an article in the April 2022 edition of Pipeline & Gas Journal. It’s titled Engineering Renewable Natural Gas Solutions, and it describes straightforward solutions to handling the numerous engineering challenges associated with customized biogas processing and biomethane utilization equipment. A summary of the article follows.

High environmental priority

Governments around the world are passing a host of regulations to drive the reduction of greenhouse gases, with particular focus on gases with high global warming potential, such as methane. An increasingly attractive solution captures methane generated from landfills and anaerobic digestion of various waste streams, upgrades it to pipeline quality biomethane, and injects it into pipelines to be used as a low carbon fuel (Figure 1).

Renewable fuel environmental credits are gained and can also be sold. Biogas/biomethane production can be a profitable enterprise, but only if the process is designed properly, the equipment is installed correctly, and the system operates reliably.

Figure 1: Biogas can be sold to natural gas pipeline operators for injection into their existing pipeline infrastructure.

Biogas can be generated from landfills and the anaerobic digestion of various waste streams, including agricultural waste, manure, wastewater, food waste, and others. While this low-pressure biogas is rich in methane, it also contains significant quantities of moisture, carbon dioxide (CO2), oxygen, and nitrogen, along with troublesome components such as hydrogen sulfide (H2S), siloxanes, and other volatile organic compounds (VOCs). The gas must also be compressed significantly to be injected into natural gas pipelines operating at hundreds and even thousands of pounds of pressure. This creates a challenge, as the authors explain:

A biogas processing facility must eliminate undesired components, raise the biogas pressure to pipeline specifications, and measure the quality of the gas. A biomethane injection skid can then verify the quality of the gas and inject the measured volume into a natural gas pipeline (Figure 2) at a safe pressure.

Figure 2: This is a generalized diagram of a biogas processing and biomethane injection system.

The custody transfer of the upgraded biogas will typically occur in the middle of the overall process, but the upstream and downstream equipment must work together to provide a reliable supply of renewable natural gas.

The biogas processing equipment condenses and removes moisture, and then uses various means to eliminate or greatly reduce H2S, siloxanes, and VOCs. The gas can then be compressed and used as a low-quality fuel—or it can undergo further processing to remove CO2, nitrogen, and oxygen—converting the biogas to biomethane. Once the gas achieves pipeline specifications, it is ready for injection into the natural gas grid.

Biomethane injection

Once a pipeline company has taken ownership of the gas, more equipment is necessary to ensure safe injection into their natural gas system. The gas must be odorized and routed through pressure regulators and flow control valves to ensure safe and reliable injection. Flow meters, pressure transmitters, and gas analysis instruments provide measurements throughout this process. These include a variety of analytical instruments that measure the energy content, as well as moisture, H2S, sulfur, CO2, oxygen, and nitrogen. Further analysis, to detect components like siloxanes, may require gas sampling for lab analysis. Isaac and Arrchana describe this critical design process:

All these analytical instruments and the control equipment must be carefully selected to handle the specific design requirements. The instruments and equipment used for biomethane injection must communicate seamlessly with the upstream processing equipment to reliably convert the biogas for sale of the resulting biomethane to the pipeline company.

Engineering and operation challenges

Designing high-performing biogas processing and biomethane injection systems can be a difficult engineering endeavor, since each application is unique, and in many cases the equipment must operate autonomously. There is no “one size fits all” solution, and each system is often customed designed for a particular application.

If any equipment is poorly selected or fails to function properly, the biomethane gas may not meet specification and must be flared or reprocessed, reducing profitability. A typical biomethane processing system may involve a multitude of vendors, making coordination difficult, and invariably leading to finger pointing when issues arise. Long term support and maintenance can be equally problematic. With critical equipment on each side of the custody transfer point, it can be difficult to troubleshoot and isolate the issue, especially when different companies own part of the process. Even when a problem’s source has been identified, it can be hard to get a particular equipment vendor to accept their responsibility and address the problem.

All these potential problems create a lengthy engineering process, uncertain timeline for project conception to production, and contentious lifecycle support.

A better way

To address these and other issues, many companies engage a limited number of partners to design and furnish the major components of the biogas system. Isaac and Arrchana explain the benefits:

Choosing a partner that can not only engineer and deliver a complete biogas processing system, but one that also specializes in the automation equipment required for safe biomethane injection, reduces project inefficiencies, and minimizes downtime for the biomethane supply.

Gas companies using this method can work with a single entity to choose the right combination of reliable, familiar equipment to supply low carbon biomethane to their system. If a problem is encountered, or if routine maintenance is required on either side of the custody transfer point, the partner can leverage their knowledge of the entire system to minimize downtime.

Potential project partners should be evaluated on their familiarity with applicable local and national codes, as well as possession of the required engineering licenses and certifications to do the work. The authors also suggest other areas for consideration:

Beyond these minimum requirements, a qualified solution provider must also have a deep knowledge of the biogas purification process and the natural gas system, know the equipment involved on both sides, and have a proven track record of successful installations.

Such a combination of skills and experience allows the partner to offer suggestions and process recommendations that help the gas company choose the best combination of equipment to meet the needs and goals of the project. The best solution providers supply most of the equipment and instrumentation directly, and they have strong partnerships with technology providers for the balance.

This type of arrangement provides equipment interoperability, high performance, and expert support. Such a solutions partner can usually furnish the critical equipment in a customized, integrated skid solution (Figure 3) that can be easily installed and commissioned on site. This significantly shortens project construction timeline and greatly simplifies system commissioning.

Figure 3: A single vendor for all biomethane injection equipment can custom engineer a process solution and deliver the entire package as an integrated, skid-mounted solution. (Courtesy of Emerson Impact Partner, Laurentide Controls.)

Case study

A large wine maker in Italy had significant agricultural and liquid wastes from their process, and they decided to install anaerobic digesters to treat the waste streams and convert them to biomethane for sale to a local energy company. The wine maker had developed the digester process, but they needed a fully integrated solution to analyze the gas product parameters, communicate with the upstream processing as required to meet specifications, and safely inject the biomethane into the nearby natural gas pipeline system (Figure 4).

Figure 4: A biomethane injection skid can receive renewable natural gas from a processing area, analyze it to confirm it meets specification, odorize it, and meter the gas for custody transfer and injection.

Since the client lacked the engineering expertise to do the work themselves, they engaged Emerson to engineer the system, construct the skid-mounted solution, install it on site, commission it, and provide ongoing operating support assistance. The skid was designed, delivered, and placed into successful production in a very compressed time schedule, quickly bringing the biogas process online and into profitable production.

Visit the Decarbonization in Natural Gas Applications section on for more on the injection of Renewable Natural Gas (Biomethane) and Hydrogen in pipeline infrastructure as an element in the transition to a carbon-neutral energy supply.

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