Abstract Biomass supercritical water gasification is clean and renewable, which can convert biomass into hydrogen rich gas. Previous studies indicated that external recycle of liquid residual could improve gas yield and gasification efficiency. However, the influence mechanism of external recycle on energy and exergy efficiency is complicated and theoretical model for system optimization is insufficient. Thermodynamic model of external recycle of liquid residual was built in this paper. Exergy efficiency of the main components and exergy loss distribution were specified and the result showed that exergy loss of reactor and preheater accounted for 26.06% and 35.88% of the total exergy loss, which were the main exergy loss sources. Effective ways to reduce exergy loss of components with large exergy loss and to improve energy and exergy efficiency of the system were proposed. Moreover, life cycle assessment of biomass gasification process was carried out. The results indicated that the increase of gasification temperature, pressure and external recycle flow rate of liquid residual and decrease of biomass concentration could improve energy and exergy efficiency of the system. Energy and exergy efficiency reached 63.67% and 48.29% respectively at the condition of gasification temperature of 560 °C, pressure of 25 MPa, recycle flow ratio of 32.43%, biomass concentration of 2.78%. Besides, the increase of gasification temperature and decrease of biomass slurry concentration and pressure could decrease GWP.

中文翻译：

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余液外循环生物质超临界水气化系统热力学及LCA分析

摘要 生物质超临界水气化清洁可再生，可将生物质转化为富氢气体。以往的研究表明，液体残渣外循环可以提高产气率和气化效率。然而，外循环对能量和火用效率的影响机制复杂，系统优化的理论模型不足。本文建立了残液外循环的热力学模型。确定了主要部件的火用效率和火用损失分布，结果表明反应器和预热器的火用损失分别占总火用损失的26.06%和35.88%，是主要的火用损失源。提出了降低火用损失较大部件的火用损失，提高系统能量和火用效率的有效途径。此外，还进行了生物质气化过程的生命周期评估。结果表明，气化温度、压力和液体残余物外循环流量的增加以及生物质浓度的降低可以提高系统的能量和火用效率。在气化温度560℃、压力25MPa、循环流量比32.43%、生物质浓度2.78%的条件下，能量效率和火用效率分别达到63.67%和48.29%。此外，气化温度的升高和生物质浆液浓度和压力的降低会降低GWP。对生物质气化过程进行了生命周期评价。结果表明，气化温度、压力和液体残余物外循环流量的增加以及生物质浓度的降低可以提高系统的能量和火用效率。在气化温度560℃、压力25MPa、循环流量比32.43%、生物质浓度2.78%的条件下，能量效率和火用效率分别达到63.67%和48.29%。此外，气化温度的升高和生物质浆液浓度和压力的降低会降低GWP。对生物质气化过程进行了生命周期评价。结果表明，气化温度、压力和液体残余物外循环流量的增加以及生物质浓度的降低可以提高系统的能量和火用效率。在气化温度560℃、压力25MPa、循环流量比32.43%、生物质浓度2.78%的条件下，能量效率和火用效率分别达到63.67%和48.29%。此外，气化温度的升高和生物质浆液浓度和压力的降低会降低GWP。残余液体的压力和外循环流量以及生物质浓度的降低可以提高系统的能量和火用效率。在气化温度560℃、压力25MPa、循环流量比32.43%、生物质浓度2.78%的条件下，能量效率和火用效率分别达到63.67%和48.29%。此外，气化温度的升高和生物质浆液浓度和压力的降低会降低GWP。残余液体的压力和外循环流量以及生物质浓度的降低可以提高系统的能量和火用效率。在气化温度560℃、压力25MPa、循环流量比32.43%、生物质浓度2.78%的条件下，能量效率和火用效率分别达到63.67%和48.29%。此外，气化温度的升高和生物质浆液浓度和压力的降低会降低GWP。