| Methanol and electricity separately are important chemical products and clean energy carriers,which play an important role in the world,and they are mostly produced by fossil fuels at present.However,its exploitation and utilization leads to many drawbacks,such as environmental pollution(haze or acid rain)and greenhouse effect(rise of sea level).Hence,investigating a cheap,clean and renewable energy is urgent.Biomass,as a renewable energy,can be directly converted into liquid fuel,including crops,wood,waste,animal manure,etc.Among all kinds of biomass utilization technologies,biomass gasification technology has been paid more and more attention because of its low pollution and high efficiency.Additionally,as a new technology developed in recent years,chemical looping technology has advantages of low energy consumption,low pollution and high economic benefits,moreover,it can be used for a variety of chemical-power processes.Herein,four different biomass gasification for methanol and power cogeneration processes,namely conventional biomass gasification for methanol and power cogeneration process(cogeneration process ?),biomass gasification integrated with chemical looping air separation for methanol and power cogeneration process(cogeneration process ?),biomass gasification integrated with iron-based chemical looping combustion for methanol and power cogeneration process(cogeneration process ?)and biomass gasification integrated with dual chemical looping technology for methanol and power cogeneration process(cogeneration process ?),were proposed and investigated from thermodynamics and environmental protection perspective.The purposes of this paper were shown below:firstly,the optimal process among the four different biomass cogeneration processes was selected;next,the parameters analysis and optimization were involved from the thermodynamic view;then,the heat exchange network was analyzed;finally,exergy balance analysis was assessed.First of all,the process descriptions of the four different biomass gasification for methanol and power cogeneration processes were disclosed.The gas-solid reaction units,including biomass gasification unit,chemical looping air separation unit(CLAS)and iron-based chemical looping combustion(Fe-CLC),were simulated by Apen Plus software.Compared the simulation results with relevant literatures,the results showed that the simulation results were consistent with the literature values,which indicated the models were accurate and reliable.After verified the reliability,the four different cogeneration processes were simulated using Aspen Plus,and the simulation results were compared based on performance indicators,which included the components of crude syngas,syngas yield,syngas ratio,methanol yield,methanol to electricity ratio,methanol efficiency,net electricity efficiency,total energy efficiency,exergy efficiency and CO2 capture ratio.The results were shown as followed:the maximum methanol to electricity ratio was obtained in the cogeneration process ?;the highest syngas yield,methanol yield and methanol efficiency were demonstrated in the cogeneration process ?;the optimal CO2 capture ratio was existed in the cogeneration process III;the highest net electricity efficiency,total energy efficiency and exergy efficiency were obtained in the cogeneration process ?.After comprehensive comparison,the optimum process was cogeneration process IV,its total energy efficiency and exergy efficiency were 63.95%and 57.93%,respectively.The parameters analysis and optimization of the cogeneration process IV were conducted.In the biomass gasification and syngas removal units,finding oxygen to biomass mass ratio(O/B,0.17-0.29)had a great impact on the system performances,steam to biomass mass ratio(S/B,0.04-0.16)only had effect on the crude syngas composition and remain system performances were almost constant,distribution ratio(Dr,0.5-0.6)had a certain influence on the system performances,and the optimum value of O/B,S/B and D,were 0.23,0.1 and 0.56,respectively.The effect of flue gas to Mn2O3 molar ratio(F/M,0-0.3)of CLAS unit on the thermodynamic performances was discussed.It was found when the F/M was 0.15,system efficiencies were the highest.For the Fe-CLC,the effect of Fe2O3 to combustible gas molar ratio(Fe/C,0.9-1.2)on the system performances was investigated,finding syngas yield was not influenced and remain indicators were changed,and system efficiencies obtained the optimal values when Fe/C was equal to 1.1.For the methanol synthesis unit,the effect of reactor temperature(Tm,190?-310?)and recycled ratio(Rr,0.92-0.98)on the system performances were analyzed.With the increase of Tm,,methanol to electricity ratio was increased,corresponding to methanol yield and system efficiencies were decreased slowly,and Tm was chosen as 230? after comprehensive considering the thermodynamic performances and reaction time.With the increasing of Rr,the decline in net electricity efficiency and the other performance indicators were risen.In addition to the thermodynamic properties,the accumulation of inert gas was also needed consideration,so Rr was chosen as 0.95.Meanwhile,the heat exchange network of cogeneration process IV was studied.The results showed that the minimum temperatures of the CLAS unit,HRSG1 and HRSG2 separately were 48.41 ?,38.47? and 11.71 ?,both of them were above the pinch point(10?),which demonstrated the rationality of this designed network.Furthermore,the exergy balance of cogeneration process IV was analyzed.It was found that the total exergy input was 558.87MW,the available exergy output was 323.78MW and the total exergy loss was 235.09MW.The energy loss of all equipments was 209.22MW,accounting for 89.00%of the total exergy loss,so the energy loss of cogeneration process IV mainly caused by its equipments.In the equipments,the energy loss of gasifier was the maximum(87.10MW),which accounted for 37.05%of the total exergy loss. |
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