Comparative Carbon Intensity Assessment for Renewable Natural Gas Transportation Options

Renewable natural gas (RNG) is associated with reduced emissions but a comparison of its transport modes is needed. For this study, carbon intensity (CI) values were calculated using the Greenhouse Gases, Regulated Emissions, and Energy Use in Transportation (GREET-2024 version) life cycle analysis model and its California version, CA-GREET 4.0. RNG transport by pipeline was found to have the lowest CI score over medium to long distances due to the high energy efficiency of the transmission network. Compressed natural gas (CNG) tube trailers had the lowest carbon intensity (3.2 gCO₂e/MJ) over shorter distances (up to 250 miles) due to minimal static emissions, but their limited payload capacity leads to higher delivery emissions (1.56 gCO₂e/MJ per 100 miles) over distances above 250 miles. As a result, liquid natural gas (LNG) trailer transport, despite having higher static emissions (10.2 gCO₂e/MJ), becomes more favorable over longer distances (above 650 miles) due to its superior delivery efficiency. These findings suggest that while CNG transport is advantageous for short hauls, pipeline transmission remains the most efficient option, with LNG trailers only becoming competitive over long distances (over 900 miles). The study provides utilities and RNG producers data to consider transport options with the lowest carbon footprint.