Numerical Simulation Analysis Of H₂O/CO₂ Hybrid Cycle Oxy-fuel Combustion System With LNG Cold Energy Utilization

Nowadays climate warming has become a global problem,and CO₂ is one of the greenhouse gas that has the greatest impact on climate change.Under the current severe environmental protection situation,the call for energy saving and emission reduction is growing stronger,countries around the world are looking for technologies to reduce CO₂emissions.Carbon capture and storage?CCS?is considered one of the most promising CO₂ emission reduction technologies,and oxy-fuel combustion is one of the reality technologies to achieve large-scale carbon capture.Natural gas is currently the main clean energy with low carbon emission coefficient.The energy saving and emission reduction effect can be more obvious by combining these two technologies.The efficiency of oxy-fuel combustion technology is encumbered by the high energy cost of air separate unit and carbon capture process.Another fact is that the liquefied natural gas contains enormous quality cold energy.Thus a novel oxy-fuel carbon capture power plant with LNG cold energy utilization is proposed in this study.LNG cold energy is used to liquefied the CO₂ to improve the system efficiency.The working fluid used for moderating combustion temperature is composed of H₂O and CO₂,and the H₂O content and CO₂ content in working fluid is adjustable.The regenerative heat of flue gas can be recovered to the most extent through adjusting the content of H₂O and CO₂.The system efficiency can be improved with zero carbon emission.The modeling and calculation is implemented by using Aspen Plus software.Some key parameters are studied to achieve the optimal efficiency.Some key parameters sensitivity are analyzed and the influence of the H₂O fraction in working fluid on system performance is studied.The results reveal that when the H₂O mass fraction is less than 0.3,the system thermal and exergy efficiency increases with the increase of the H₂O content in the working fluid.When the H₂O mass fraction in the working fluid rises over 0.3,the system thermal and exergy efficiency decreases with the increase of H₂O content due to the decrease of the recycling heat carried by H₂O.The thermal and exergy efficiency reach the maximum value at 58.3%and 41.6%when the H₂O mass fraction is 0.3.Compared to dry cycle,the system thermal and exergy efficiency of the proposed system is increased by17.3%and 21.4%,respectively.