Equipment capacity matching methodology and techno-economic analysis for a novel low-carbon multi-energy system with the integration of oxy-coal combustion power plant and power-to-gas

Oxy-fuel combustion (OFC) is a promising technology for CO2 capture, utilization and storage (CCUS), but the high energy consumption of oxygen generation limits its application. Power-to-Gas (PtG) allows to use excess production from wind or solar power, and thus enables capabilities to balance fluctuations from renewable energy generation, but requires CO2 as a synthetic feedstock and produces large amounts of byproduct oxygen. Integration of the two technologies can reduce the energy consumption of the OFC for oxygen production and provide CO2 for PtG, improving their techno-economics. A low-carbon multi-energy system with the integration of PtG and oxy-coal combustion power plant was first proposed to make full use of byproduct oxygen for oxy-coal combustion boiler (OCCB) from green hydrogen production of water electrolysis and to synthesize renewable fuels from green hydrogen and captured CO2. And then the capacity matching methodology of the main components was proposed to achieve multi-energy gradient utilization of electricity, heat and synthetic fuel chemical energy, and the internal integration of hydrogen, oxygen, CO2 and water. Two system schemes were proposed and simulated with the detailed models built with Aspen Plus and Matlab softwares. The energy and exergy analyses show that implementing Scheme 2 that uses CO2 compression and purification unit (CPU) and recovers waste heat from water electrolysis can increase renewable natural gas (RNG) product purity, total energy efficiency, and exergy efficiency by 9.4 %, 20.0 %, and 2.6 % compared to Scheme 1 with combustion deoxygenation, respectively, reaching 97.7 %, 67.4 %, and 51.7 %. Based on the capacity matching methodology, the capacity ratio of proton exchange membrane electrolysis cells to oxy-coal combustion boiler (PEMEC-OCCB) is 3.45 and the capacity ratio of RNG synthesis to oxy-coal combustion boiler (RNG-OCCB) is 0.72. Besides, the RNG production cost is estimated as 1610 $/t exceeding the current market price of natural gas, and it will be lower than the current market price when the PEMEC equipment prices drop to $250/kW in the future. The calculated results of the capacity matching methodology and techno-economic analysis can provide the guideline for the design and equipment selection of the low-carbon multi-energy system with the integration of oxy-coal combustion power plant and Power-to-Gas.