Analysis and prediction of hydrogen-blended natural gas diffusion from various pipeline leakage sources based on CFD and ANN approach

The influences of pipeline leakage source types on the hazard area distribution caused by accidental hydrogen-blended natural gas leakage are still the focus of gas leakage accidents. Three types of pipeline leakage sources are discussed in this study. Namely, the gas in the vertical pipeline flows from top to bottom, and the leakage orifice is in the pipeline wall; the gas in the vertical pipeline flows from bottom to top, and the leakage orifice is in the pipeline wall; the leakage orifice is in the horizontal pipeline end. The common feature of the above three pipeline leakage sources is that the normal of leakage orifice is parallel to the horizontal plane. The differences in the flow field distribution of hydrogen-blended natural gas released from three pipeline leakage sources are compared through numerical simulation. The effect of various factors on the jet centerline, concentration decay, and maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are analyzed. The predictive models of hydrogen-blended natural gas's maximum horizontal diffusion distance in three pipeline leakage sources under multi-factor coupling are established through a backward propagation neural network (BPNN). Results show that the angle between the gas flow direction in the pipeline and the normal of the leakage orifice, and the background step flow cause differences in the concentration field near the leakage orifice from the three pipeline leakage sources at the same working conditions. In the near-field region, the leakage orifice diameter has the most significant influence on the jet centerline of three hydrogen-blended natural gas jets among three factors. The concentration decay rate of gas released from the horizontal pipeline end is greater than that of gas released from the other two pipeline leakage sources. With the increase of volumetric flow rate, the maximum horizontal diffusion distances of methane released from three pipeline leakage sources all increase, while the maximum horizontal diffusion distances of hydrogen released from three pipeline leakage sources have little change. The predictive models of the maximum horizontal diffusion distance of hydrogen-blended natural gas released from three pipeline leakage sources are established through BPNN. The maximum horizontal hazard distances of the new working conditions are predicted, and the predicted results are in good agreement with the numerical simulation results. This investigation has guiding value for fast and accurate prediction of flammable gas hazard areas.