Abstract:

A new kind of coal gasification based on Zn/ZnO redox pair via a two-step cycle is proposed.Firstly，coal is mainly gasified to CO by reacting with ZnO in a highly endothermic step at about 1200℃.Secondly，in an exothermic step at a lower temperature of about 500℃，hydrogen gas and solid ZnO are produced via the hydrolysis of liquefied zinc produced from the first step.The produced ZnO can be then recycled to the first step.In this paper，both the auto-thermal reactor with partial oxidation of coal and solar reactor were considered as heat supply in the first step.The theoretical energy analysis of the new system based on the 1st and the 2nd law of thermodynamics was performed.The result showed that the system could reach an ideal thermal efficiency as high as 89% when equipped with the auto-thermal reactor，and 67% when solar reactor was used considering the current thermal efficiency of solar collector.The relative exergy efficiencies were 80% and 66% respectively.The major sources of exergy losses came from the irreversibility of reaction in auto-thermal reactor，and heat losses from solar reactor.A simple environmental evaluation for the system was also performed based on the ratio of produced CO to H₂（CHR）in the system.Apparently，the solar heated system was more environmentally friendly than the auto-heated system，the CHR of the former was smaller than 1/6 of the latter.

摘要： 本文以基于Zn/ZnO的两步式热化学循环为基础构建了一种新型的煤气化系统。该系统流程主要由两步构成：首先煤与ZnO在高温下发生吸热反应，气化生成CO气体和锌蒸汽。锌蒸气经冷凝后自动从混合气体产物中分离出来被送入下一步反应中与水发生放热反应，生成氢气和ZnO固体。ZnO又可被回收进行第一步反应。本文在设计第一步反应供热系统时分别考虑了煤部分氧化自热和太阳能加热两种方式，并对基于这两种加热方式的新型煤气化系统分别进行了理论能效评估和环境性能评估。评估结果显示：自热式煤气化系统的理想热效率和火用效率分别达到了89％和80％；而按现有太阳能加热系统的热效率计算，太阳能加热式煤气化系统的整体理想热效率和火用效率最高分别可以达到67％和66％。从环境性能上来看，太阳能加热式煤气化系统远远优于自热式系统，前者的CHR（产CO与产H2比）不到后者的1/6。