Feasibility analysis on the transportation of hydrogen-natural gas mixtures in natural gas pipelines

Hydrogen that is mixed with natural gas at a certain proportion is used as a domestic fuel, which is one of the ways to reduce greenhouse gas emission. And one feasible method is to use the existing developed natural gas pipeline networks to transport hydrogen-natural gas mixtures (HCNG) to end-users. However, hydrogen and natural gas are different in physical and chemical properties, and HCNG may have greater negative effects on end-users and pipeline transportation conditions. To address this concern, the gas interchangeability and combustion characteristics of natural gas at different hydrogen mixing ratios were analyzed using the Delbourg method, Weaver method, Wobbe index, and calorific value method. A pipeline model was established based on the HYSYS software and similarity principle, and the influence of hydrogen adding on the working conditions of natural gas pipelines and compressors was studied. With the increase of the volume fraction of hydrogen in HCNG, the thermal load of a gas appliance decreased, the flame propagation speed of gas increased sharply and the tempering risk of the gas appliance increased. Hydrogen addition increased the gas transmission capacity of a pipeline, but the pressure and flow rate corresponding to its equilibrium operating point dropped when the pipeline network and compressors were operated jointly, which led to the reduction of gas transmission capacity instead.