Study On The Co-firing Of Gasified Biofuel In A Natural Gas Combined Cycle Based On Oxy-fuel Combustion

With the the increasing concern of global warming,it is urgent to reduce carbon emissions.Seeking for highly efficient renewable energy utilization technologies and introducing carbon capture and storage（CCS）technologies are effective methods.In this paper,the flue gas from combustion was utilized as gasifying agents,thus the biomass gasification was integrated with the natural gas combined cycle based on oxy-fuel combustion.The Aspen Plus,a chemical process simulation software was used to establish the system model.The effects of different gasifying conditions on biomass gasification process,syngas-natural gas co-firing process and power generation process based on oxy-fuel combustion were investigated.The effects of different gasifying agents,gasification temperature and pressure on output of important components in the syngas,syngas heating value,gasification efficiency and the biggest mixing ratio of syngas to natural gas were stidied.Furthermore,the net power generation efficiency with the biggest mixing ratio of syngas to natural gas under different gasification atmospheres were investigated.The results showed that the mixing ratio of syngas to natural gas under steam+O₂ gasification,steam gasification steam+CO₂+O₂ gasification,CO₂+O₂ gasification,steam+CO₂ gasification and CO₂gasification was 0.40,0.50,0.54,0.55,0.71 and 0.71,respectively,and the corresponding net power generation efficiency was 39.4%,35.2%,34.6%,34.3%,26.5%and 26.0%.When steam+O₂ was employed as gasifying agent,the net power generation efficiency decreased at first and then increased with the rise of the gasification temperature,and it showed a constant growth with the rise of gasification pressure.When the gasification temperature was 600℃and pressure was 3.5 MPa,the net power generation efficiency reached the highest value,which was 40.34%.To better evaluate the system performance,the study divided the overall system based on steam+O₂ gasification into four subsystems:biomass gasification,gas turbine,heat recovery steam generator and carbon capture subsystems.The exergy analysis was carried out,and the results revealed that the gas turbine based on oxy-fuel combustion possessed the highest exergy efficiency,which was 85.15%,and its exergy destruction was also the highest among the four subsystems,which accounted for 54.52%of the total exergy destruction of the overall system.The exergy efficiency was the lowest in biomass gasification subsystem,which was 51.14%.