Comprehensive Assessment And Multi-objective Optimization For Energy System With CO₂ Capture

The global climate change resulting from the emissions of greenhouse gas(GHGs) is an important and serious global environmental problem facing by human being to date.The GHGs making the greatest contribution for the global temperature rise is carbon dioxide(CO₂)so it becomes the chief GHGs to be solved.It is known that the energy system adopted technology of CO₂ capture and storage(CCS)is significant for reducing CO₂ emissions.Supported by the NSF of China(No.50520140517),this paper studies the comprehensive assessment and multi-objective optimization for energy system with CCS,including the comprehensive technical and economic analysis methods,integration of a novel energy system and comprehensive analysis and multi-objective optimization on a polygeneration system with CCS.Based on summarization and comparative analysis on the existing evaluation criterion for CO₂ reduction,a new comprehensive technological and economic analysis method is proposed for energy system with CCS.In the new method,the correlation expressions of the cost of CO+2 avoided and the energy and investment penalty are built. It is pointed out that an important resolution to reduce the cost of CO₂ avoided is to improve the technical performance of system so that reduce the energy penalty.The important role that system integration plays in CO₂ avoidance is analyzed. Based on comparative analysis with conventional CO₂ capture system,the characteristics of chemical and power poly-generation system with CCS are analyzed.It is found that system integration can achieve the goal of reducing the cost of CO₂ avoided greatly,through reducing the energy penalty and the investment in CO₂ recovery process,and saving the energy consumption and the investment of production process.A novel integrated system of clean fuel production,air separation unit(ASU) cryogenic energy utilization and CO₂ recovery is proposed.Based on the integration principle of greenhouse gas control,the production process of clean fuel,ASU and CO₂ recovery process are integrated.That is to enhance the concentration of CO₂ in the mixed gas by the clean fuel production process,and to realize the rational utilization of cryogenic energy through the integration of ASU and CO₂ recovery process.Meanwhile, the clean fuel production is promoted by rational utilization of purge gas of CO₂ recovery process.Therefore,the energy penalty of CO₂ recovery can be reduced effectively,and the energy consumption of clean fuel production is expected to be reduced too.The comprehensive performance of the novel polygeneration system with CCS is analyzed,and then the multi-objective optimization on this system is carried out.The comprehensive technical and economic analysis on the novel system reveal that the energy penalty can be negative when the rate of CO₂ avoided reaches to 90%～95.7%, while the investment only increases about 6%～33%than the reference system,finally the cost of CO₂ recovery is only 1.3～5.8 $/tCO₂,which means that the near-zero cost of CO₂ avoidance can be achieved.The multi-objective optimization results show that the process and parameters resulting from multi-objective optimization are different from those of single object optimization,and the multi-objective optimization can further reduce the cost of CO₂ avoided and enhance the comprehensive performance of the system through considerations of system thermal,economic,and environmental performances all together.