As the global shift toward decarbonization accelerates, Renewable Natural Gas (RNG) has emerged as a cornerstone of the circular economy. However, moving biogas from a landfill or anaerobic digester into a commercial pipeline isn’t a “one-size-fits-all” process. It requires a highly specialized, custom-engineered gas compression package.
At Dearing Compressor, we specialize in the “Midstream” of RNG – taking processed gas and boosting it to the precise pressures required for pipeline injection. Here is a look at the critical design considerations for these systems.
Why Customization is Non-Negotiable for RNG
Unlike traditional natural gas, RNG source conditions can vary wildly depending on the feedstock (dairy manure, food waste, or landfill gas). A custom package ensures that the compression technology matches the specific flow rates and chemical composition of your site.
Key Components of an RNG Compression Package
To achieve reliable RNG process, several systems must work in perfect synchronization:
● The Feed Compressor: Typically a low-pressure blower, rotary vane, or screw compressor used to pull RNG from the biodigester or landfill and feed the RNG process equipment.
● Filtration & Separation: RNG must be free of moisture and corrosive constituents to protect the pipeline and facilitate commercial use of the RNG.
● The Injection Compressor: Usually a reciprocating compressor or a high-pressure rotary screw, designed based on required system pressures and system flow rate.
● Gas Cooling Systems: Compression generates heat. Multi-stage cooling is essential to meet the pipeline’s maximum temperature requirements.
● PLC Control Systems: Advanced automation that monitors gas quality (methane content) and pressure in real-time, ensuring the system shuts down if gas doesn’t meet “pipeline quality” specs.
Critical Design Considerations for RNG Injection
1. Matching Discharge Pressure to Pipeline Requirements
Pipeline pressures can range from 100 PSIG to over 1000 PSIG, depending on whether you are injecting into a local utility distribution line or a high-pressure transmission header.
● Low Pressure: Often uses rotary screw technology for high volume and steady flow.
● High Pressure: Requires multi-stage reciprocating compressors to reach the necessary compression ratios efficiently.
2. Materials of Construction and Gas Composition
Depending on the service of the compressor, care must be taken when selecting materials for construction. In the water-saturated feed stream, RNG is corrosive and requires specialized coatings and stainless-steel components to prevent premature wear and ensure a 20+ year equipment lifespan. Injection or product gas compressors typically process pipeline-quality natural gas, and standard materials of construction can be used.
3. Footprint and Portability
Many RNG projects are located in remote agricultural or municipal areas. Designing the package on a skid-mounted, modular frame allows for factory testing and “plug-and-play” installation, reducing expensive on-site labor and construction time.
Challenges in RNG Compression
Designing these systems isn’t without hurdles. Engineers must account for:
● Variable Inlet Pressure and Flow: As digester output fluctuates, the compressor must be able to “turndown” without losing efficiency.
● Strict Interconnect Standards: Utility companies have zero tolerance for gas that doesn’t meet their specific thermal or purity standards.
Expert Tip: Incorporating a Variable Frequency Drive (VFD) into your RNG package allows the system to scale its energy use based on real-time gas production, significantly lowering your operational expenses (OPEX). A VFD also reduces motor starting inrush current, which is helpful in remote areas where power availability is a concern.
Why Choose Dearing Compressor?
Designing a custom RNG compression package is a balance of mechanical engineering, chemical compatibility, and regulatory compliance. At Dearing Compressor and Pump Co., we bring decades of experience in gas handling to the renewable sector, helping you move gas safely and efficiently from the source to the pipeline.
Are you planning an RNG project? Contact our team of engineers and professionals today to discuss your specific flow and pressure requirements.
