摘要
【目的】考察低氧烘焙对杉木屑品质、热解特性、30 d储藏过程中品质变化和醛酮类气体生成行为的影响,为低氧烘焙杉木屑作为燃料和热解工艺原材料的产品品质、热解动力学的基础信息和工业应用中的风险控制提供参考。【方法】将杉木屑在含0%~9%vol O2的氮气中烘焙并进行工业分析、元素分析和纤维素分析,使用氧弹量热仪、SEM、TGA、色差计和GC-MS分析其热值、微观结构、热解特性、色差和脂肪酸,将样品放入半封闭式储藏反应器中储藏30 d,使用HPLC等分析醛酮类气体的生成行为,利用多元线性回归分析颜色与品质、烘焙载气含氧量与醛酮类气体释放动力学之间的关系。【结果】随着烘焙的发生和烘焙载气含氧量从0%增加至9%,烘焙杉木屑表面出现小孔且管状结构清晰,热值从19.82 MJ·kg^(-1)增加至28.25 MJ·kg^(-1),活化能从131.32 kJ·mol^(-1)减少至101.68 kJ·mol^(-1)。经低氧烘焙后杉木屑的H/C和O/C减少,但烘焙载气含氧量对H/C和O/C的影响很小。根据多元线性回归分析,C、H、O元素和木质素含量与颜色的相关性显著(R2>0.96)。低氧烘焙可以通过减少杉木屑的吸水性,从而使30 d储藏过程中干物质的损失、颜色变化和品质的不利变化减少。随着烘焙载气含氧量从0%增加至9%,烘焙杉木屑脂肪酸含量从644.0μg·g^(-1)减少至369.5μg·g^(-1),使得醛酮类气体释放总量从11.84μg·g^(-1)减少至2.89μg·g^(-1),但仍然高于杉木屑的释放总量(1.40μg·g^(-1))。在30 d储藏过程中,杉木屑主要释放乙醛、己醛和丙酮,烘焙杉木屑主要释放丁醛、丙酮和丙醛,而低氧烘焙杉木屑主要释放丁醛和丙醛,且均在前5 d集中释放并在第30天仍持续释放。建立了烘焙载气含氧量与醛酮类气体释放动力学的多元线性回归关系。【结论】低氧烘焙行为可提高杉木屑的燃料性质,颜色变化可以在一定程度上反映其成分和质量的差异,低氧烘焙使烘焙产物进行热解反应的所需能量减少,热解反应体系更加均匀,工业中热解行为的调控更加有效。低氧烘焙可有效降低烘焙杉木屑在储藏过程中品质的不利变化,并降低75.5%的烘焙杉木屑醛酮类气体释放总量,从而降低工作人员和用户的健康风险。
【Objective】The effects of low-oxygen torrefaction on fuel properties,pyrolysis characteristics,properties’variation and release of aldehydes and ketones gas during 30 days of storage were examined.It provides product quality,basic information of pyrolysis kinetics and risk control in industrial applications for low-oxygen torrefied Chinese fir sawdust as fuel and raw materials for pyrolysis processes.【Method】Chinese fir sawdust was torrefied in nitrogen containing 0%-9%vol oxygen,and analyzed via industrial analysis,elemental and cellulose analysis.The higher heating value,microstructure,pyrolysis characteristics,color value and fatty acid were analyzed using oxygen bomb calorimeter,SEM,TGA,colorimeter and GC-MS,respectively.The sample was stored in semiclosed storage reactor for 30 days,while the released aldehyde/ketone gas was analyzed by HPLC.The relationship between color and properties,oxygen content of carrier gas during torrefaction and the kinetics of aldehyde/ketone release were analyzed by multiple linear regression.【Result】With the occurrence of torrefaction and the increase in the oxygen content of carrier gas from 0%to 9%,the surface of torrefied Chinese fir sawdust forms small holes and a clear tubular structure.The heating value of torrefied sawdust is increased from 19.82 MJ·kg^(-1) to 28.25 MJ·kg^(-1),while its activation energy is reduced from 131.32 kJ·mol^(-1) to 101.68 kJ·mol^(-1).After torrefaction,the H/C and O/C of Chinese fir sawdust are reduced.The oxygen content of carrier gas during torrefaction does not affect the H/C and O/C.According to multiple linear regression analysis,C,H,and O elements and lignin content are significantly correlated with color value(R^(2)>0.96).Low-oxygen torrefaction can reduce the water absorption of Chinese fir sawdust,thereby reducing the loss of dry matter,color changes and adverse changes in quality during 30-day storage.With the increase in the oxygen content of the carrier gas from 0%to 9%,the fatty acid content of Chinese fir sawdust is decreased from 644.0μg·g^(-1) to 369.5μg·g^(-1).The amount of aldehydes/ketones emission is decreased from 11.84μg·g^(-1) to 2.89μg·g^(-1) during the process of 30 days storage with the increase in the oxygen content of the carrier gas from 0%to 9%,which is still higher than that released from Chinese fir sawdust(1.40μg·g^(-1)).Meanwhile,compared with the emission compounds from Chinese fir sawdust of ethanal,hexanal and acetone,the torrefied Chinese fir sawdust mainly releases butanal,acetone and propanal,while low-oxygen torrefied Chinese fir sawdust mainly releases butanal and propanal.All samples release aldehydes and ketones intensively during the first 5 days,and continue to release on the 30th day.A multiple linear regression relationship between the oxygen content of carrier gas during torrefaction and the kinetics of aldehydes/ketones release is established.【Conclusion】The low-oxygen torrefaction behavior improves the fuel properties of sawdust.The color reflects the differences in composition and quality.Low-oxygen torrefaction reduces the energy requirement for the pyrolysis reaction of Chinese fir sawdust,improving the pyrolysis reaction system more uniform,and improves the pyrolysis behavior in industry more effectively.In this study,oxidative torrefaction can effectively reduce the adverse changes in the properties and 75.5%of the total aldehydes/ketones gas released from torrefied Chinese fir sawdust during storage,thereby reducing the health risks of workers and residents.
作者
唐致远
袁兴中
曹亮
奚燕妮
黄忠良
李辉
TANG Zhiyuan;YUAN Xingzhong;CAO Liang;XI Yanni;HUANG Zhongliang;LI Hui(Key Laboratory of Environmental Biology and Pollution Control and College of Environmental Science and Engineering,Hunan University,Changsha 410082,Hunan,China;Institute of Biological and Environmental Engineering,Hunan Academy of Forestry,Changsha 410004,Hunan,China;State Key Laboratory of Utilization of Woody Oil Resource,Changsha 410004,Hunan,China)
出处
《中南林业科技大学学报》
CAS
CSCD
北大核心
2021年第3期157-169,共13页
Journal of Central South University of Forestry & Technology
基金
湖湘青年英才支持计划项目(2018RS3109)
长沙市杰出创新青年培养计划项目(kq1802010,kq1802040)
湖南省林业科技创新杰出青年项目(XLK201938,XLK201908)。
关键词
杉木
烘焙
储藏
动力学
品质
Chinese fir
torrefaction
storage
kinetics
property
