Network Modeling and Operation Optimization of Electricity-HCNG-Integrated Energy System

Hydrogen-enriched compressed natural gas (HCNG) has great potential for renewable energy and hydrogen utilization. However, injecting hydrogen into the natural gas network will change original fluid dynamics and complicate compressed gas's physical properties, threatening operational safety of the electricity-HCNG-integrated energy system (E-HCNG-IES). To resolve such problem, this paper investigates effect of HCNG on gas network dynamics and presents an improved HCNG network model, which embodies the influence of blending hydrogen on the pressure drop equation and line pack equation. In addition, an optimal dispatch model for the E-HCNG-IES, considering the "production-storage-blending-transportation-utilization" link of the HCNG supply chain, is also proposed. The dispatch model is converted into a mixed-integer second-order conic programming (MISOCP) problem using the second-order cone (SOC) relaxation and piecewise linearization techniques. An iterative algorithm is proposed based on the convex-concave procedure and bound-tightening method to obtain a tight solution. Finally, the proposed methodology is evaluated through two E-HCNG-IES numerical testbeds with different hydrogen volume fractions. Detailed operation analysis reveals that E-HCNG-IES can benefit from economic and environmental improvement with increased hydrogen volume fraction, despite declining energy delivery capacity and line pack flexibility.