固体燃料熔融盐热转化研究进展

The review on the solid fuel conversion by molten salt

以煤、生物质和固体废物为代表的固体燃料热解制油与气化制气具有很好的应用前景,是目前研究热点。常规热解反应器存在传热不均、易结焦和传热效率低等缺点,会导致热解温度升高、油产率降低以及需要频繁清焦等一系列问题。为了克服上述问题,学术界提出了以熔融盐作为直接传热介质进行固体燃料热转化的技术路线,以期提高传热传质效率、降低裂解温度,实现目标产物最大化。研究表明:(1)熔融盐介质具有更优的传热传质性能,能够降低热解活化能,抑制热解反应过程中有害气体的释放,并将其他有害金属元素保留在熔融盐内,从而高效解决硫化物、卤化物和重金属排放等问题。(2)探讨了熔融氯化盐和熔融碳酸盐对于固体燃料热解的作用机制:相比于腐蚀性更强的氯化盐体系,熔融碳酸盐具有较好的热稳定性和催化活性,并且能够原位催化脱除固体燃料中的杂原子。(3)在熔融盐气化方面,碳酸盐同样表现优越;相比于单一碳酸盐,混合碳酸盐体系气化催化活性更高;但熔融盐气化温度低,造成气化气中焦油含量增加等问题;在熔融盐中引入Ni等过渡金属能够克服上述问题,提高合成气产率,实现制取富氢合成气的目的。(4)目前熔融盐的回收再利用主要通过盐冷却、水洗沉淀、过滤和干燥等技术路线,固体燃料热解和气化后熔融盐的低成本回收利用仍需进一步深入研究。

The pyrolysis and gasification of solid fuels such as coal,biomass,and solid waste are currently hot research topics with promising applications.However,conventional pyrolysis reactors suffer from uneven heat transfer,clogging,and low heat transfer efficiency,leading to high pyrolysis temperatures,reduced pyrolysis yields,and the need for frequent decoking.To address this issue,a technical approach using molten salts as a direct heat transfer medium for thermal conversion is proposed,which can improve heat transfer efficiency,lower pyrolysis temperatures,and maximize the yield of target products.(1)Molten salt pyrolysis,due to its superior heat and mass transfer characteristics,can reduce the activation energy of pyrolysis and inhibit the release of harmful gases during the pyrolysis reaction.Simultaneously,it retains other inorganic substances and metals within the salt,thus effectively addressing issues such as emissions of sulfides,halides,and heavy metals.(2)For different molten salt systems,the mechanisms of chloride and carbonate salts in the pyrolysis of solid fuels are discussed.Compared to chloride salt systems,which are more corrosive,molten carbonate salts not only exhibit better stability and catalytic activity but also catalytically remove heteroatoms from solid fuels in situ.(3)Molten carbonate salts can also be used for the gasification of solid fuels.Among them,the gasification catalytic activity is highest in the three-component mixed carbonate salt system.However,molten salt gasification occurs at lower temperatures,which may lead to an increase in tar content in the gas.The introduction of transition metals such as Ni into molten salts promotes gasification conversion rates,increases syngas yields,and achieves the production of hydrogen-rich synthesis gas.(4)Currently,the recovery and treatment of molten salts mainly involve processes such as salt cooling,water washing precipitation,filtration,and drying.However,further research is needed to explore low-cost recycling and utilization of molten salts after solid fuel pyrolysis and gasification.