Research On The Manganese Based Chemical Looping Air Separation Technology And Its Application In IGCC System

Integrated gasification combined cycle?IGCC?is considered to be the most promising coal-based clean power generation technology in the 21st century.But the cryogenic air separation method for supplying pure oxygen is complicated,energy-intensive and costly.As a novel oxygen generation technology,chemical looping air separation?CLAS?has the advantages of simplicity and high efficiency.It can be integrated with the IGCC to improve the system efficiency.At the same time,efficient carbon capture is an important way to reduce carbon emissions for IGCC and greenhouse gas emissions.Therefore,in this work,the promising oxygen carrier for CLAS and the characteristics of CLAS system are firstly studied.Then CLAS is applied to IGCC system coupled with different carbon capture methods to study the operating characteristics of each system.Firstly,the reactivity and cycle stability of Mn-based oxygen carriers are studied by thermogravimetric experiments.The mechanism function and kinetic parameters of oxygen-absorbing and oxygen-releasing processes are determined by kinetic analysis.The results show that Mn₂O₃/Zr O₂ has good reactivity and cycle stability,which is suitable for CLAS process.With the increase of reaction temperature,the reduction rate of the oxygen carrier increases significantly,while the oxidation rate decreases obviously.By the kinetic analysis of Mn₂O₃/Zr O₂,the mechanism function of the reduction is determined as the Avrami-Erofeev random nucleation and subsequence growthrandom nucleation and subsequent growth?A2?model.The corresponding apparent activation energy and pre-exponential factor are 180 k J/mol and 1.98×10⁸min^-1,respectively.The mechanism of oxidation is the phase boundary reaction?R3?model.The corresponding apparent activation energy and pre-exponential factor are 228k J/mol and 5.32×10¹¹ min^-1,respectively.It is also found that the reaction order is detected to increase exponentially with temperature for the oxidation reaction.Secondly,the obtained chemical reaction kinetics model of Mn₂O₃/Zr O₂is coupled with the gas-solid flow hydrodynamics model.A one-dimensional CLAS model of dual fluidized bed is established.The oxidation reactor and the reduction reactor are modeled by a fast fluidized bed and a bubbling fluidized bed,respectively.The effects of oxidation temperature,reduction temperature,air volume flow rate and CO₂ volume flow rate on the oxygen mole fraction and the specific power consumption?SPC?are studied.The results show that the oxygen mole fraction increases with the increment of reduction temperature and air volume flow rate.SPC decreases with the increase of reduction temperature and CO₂ volume flow rate.Lower SPC can be reached when the oxidation and the reduction reactor temperatures are closer.SPC is 0.07555 k Wh/m³ at the oxidation and reduction temperatures of 770°C,the air flow rate of 50 Nm³/h,and the CO₂ flow rate of 23 Nm³/h,which is much lower than that of the conventional cryogenic air separation system.Thirdly,CLAS is applied to the IGCC system and the model of CLAS-IGCC system is established.The main models in the system are validated.The effects of the main operating parameters of oxygen to coal mass ratio(R_OC),water to coal mass ratio(R_SC)and reduction reactor temperature(T_RR)on the raw syngas composition,cold gas efficiency and system efficiency are studied.The results show that when the gasification temperature,gasification pressure,R_OC,and R_SC are 1315 ^oC,24 bar,0.8 and 0.06respectively,the molar fraction of H₂+CO in raw syngas is the highest.With R_OC,R_SCand T_RR of 0.75,0.06 and 770 ^oC,the CLAS-IGCC system achieved high cold gas efficiency and system efficiency of 81.79%and 50.86%,respectively.Finally,based on the CLAS-IGCC system,the models of CLAS-IGCC system with monoethanolamine?MEA?post-combustion method,Selexol pre-combustion method,chemical looping combustion?CLC?method and calcium looping process?CLP?method carbon captures are established,respectively.The effects of the main operating parameters on the characteristics of each system are studied,and the energy balance and exergy balance are calculated for each system.The results show that when the R_OC,R_SCand T_RR are kept at 0.75,0.06 and 770°C respectively,the energy and exergy efficiencies of CLAS-IGCC system with MEA post-combustion carbon capture are40.20%and 37.70%,respectively.The energy and exergy efficiencies of CLAS-IGCC system with Selexol pre-combustion carbon capture are 43.65%and 40.94%,respectively.The energy and exergy efficiencies of CLAS-IGCC-CLC system are 46.32%and 43.44%,respectively.The energy and exergy efficiencies of CLAS-IGCC-CLP system are 45.04%and 42.25%,respectively.It can be seen that the CLAS-IGCC system with CLC carbon capture has high energy efficiency and exergy efficiency as well as high carbon capture efficiency.For the CLAS-IGCC system with MEA post-combustion carbon capture,the maximum energy loss and exergy destruction are present in the CO₂ capture and gas turbine subsystems respectively,accounting for41.64%of the total energy loss and 42.58%of the total exergy destruction of the system.For the CLAS-IGCC system with Selexol pre-combustion carbon capture,the maximum energy loss and exergy destruction occur in the cleaner subsystem containing pre-combustion carbon capture and gas turbine subsystem respectively,contributing up to 31.95%of the total energy loss and 43.09%of total exergy destruction of the system.The maximum exergy destruction of the CLAS-IGCC-CLC system is present in the CLC unit,occupying up to 31.50%of the total exergy destruction.And the maximum exergy destruction of the CLAS-IGCC-CLP system occurs in the gas turbine unit,accounting for 34.39%of the total exergy destruction.Therefore,optimization should be focused on these components to improve the system efficiency.