Numerical simulation of throughput enhancement in natural gas pipelines via direct LNG injection

Advancing pipeline transmission technology is critical for ensuring a stable energy supply. This study proposes an innovative scheme involving the direct injection of pressurized Liquefied Natural Gas (LNG) into pipelines. This scheme simplifies traditional regasification processes and utilizes the thermal energy of the pipeline gas to enhance transmission capacity. Inadequate thermal mixing during cryogenic LNG injection may lead to risks such as localized low temperatures and material failure within the pipeline. Investigating the thermal mixing characteristics and temperature distribution post-injection is therefore significant. Consequently, based on numerical simulation methods, this study investigates the dispersion patterns of LNG after injection and its impact on pipeline wall temperature. Strategies such as replacing pipe sections with low-temperature-resistant material and controlling branch pipe structural parameters are employed to address localized low-temperature issues. The results demonstrate that the LNG injection ratio has a pronounced effect on mixing dynamics and wall temperature. Increasing the injection ratio from 0.5% to 5% leads to a 67.9% reduction in the minimum outlet temperature. For the operating conditions studied with an injection ratio below 5%, retrofitting only the initial 10-m section with cryogenic-resistant material is adequate. Regarding branch pipe configuration, optimal mixing occurs at one-quarter of the pipe diameter, raising the minimum wall and outlet temperatures by 21.09 °C and 4.76 °C, respectively, compared to a half-diameter insertion. Furthermore, increasing the branch pipe diameter effectively mitigates the thermal impact of LNG on the pipe wall. This study provides an economical and reliable solution for enhancing the capacity of existing pipeline networks.