【作者】 林晓芬；

【导师】 张军；

【作者基本信息】 东南大学 ， 热能工程， 2006， 硕士

【摘要】 烟气中所含的二氧化硫和氮氧化物是大气污染的主要物质,如何经济有效的去除烟气中的二氧化硫和氮氧化物引起了全世界研究人员的重视。目前为止,已经出现了多种的脱硫脱氮方法,而活性炭法由于能够同时去除烟气中的二氧化硫和氮氧化物、吸附剂可以再生等优点而受到广泛的关注。但活性炭的市场成本高,难以满足大规模使用的需要。寻找价格低廉而吸附效果好的吸附剂一直为各国研究人员所努力。基于生物质能有效利用的目的,我们提出了一种将生物质能利用与燃煤污染控制相结合的生物质能利用的新方法,在这一方法中生物质热解焦作为吸附剂被用来脱除烟气的SO2和NO。本文中我们对生物质焦吸附SO2和NO的性能进行了研究。研究中我们选用了8种生物质。为了解热解条件对焦样吸附性能的影响,制焦时采用了400℃、500℃、600℃、850℃等4个不同的热解温度,快速和慢速两种热解速度,和10分钟、20分钟、30分钟等3种不同的热解保持时间。为了解生物质焦的结构特征,采用扫描电子显微镜分析了其表面形态,采用傅里叶红外光谱仪分析了其表面化学组成,采用氮吸附法和压汞法测量焦样的孔隙结构,得到焦样的比表面积和孔径分布。为了研究生物质焦的吸附效率,搭建了小型的实验平台,用生物质焦进行了分别吸附模拟干烟气中二氧化硫、一氧化氮和同时吸附SO2/NO的实验,用烟气分析仪记录模拟烟气中SO2、NO浓度随时间关系曲线。将生物质焦吸附能力与活性炭进行了对比。最后分析了各种因素对生物质焦吸附能力的影响。扫描电镜实验结果表明,生物质在制焦后,表面粗糙度提高,比表面积增大,孔隙更加发达。生物质焦样的FTIR曲线上主要有二氧化硅SiO2、草酸根、炭酸根、羟基、甲基亚甲基的吸收峰;随着热解温度的升高,焦样炭化程度提高,表面有机官能团含量减少。氮吸附法主要测量中微孔部分的孔隙结构,而压汞法主要测量大孔和靠近大孔的部分中孔的孔隙结构。实验结果表明,氮吸附法测得焦样比表面积差别较大,其值在0.1～400m2/g之间,压汞法测得焦样比表面积差别相对较小,其值分布在10～60m2/g之间。生物质焦的微孔主要集中在0.8-1.5nm和1.8-3.5nm范围内;生物质焦的中孔和大孔则在10nm-60nm和60-600nm范围出现两个主要的分布峰。热解温度对焦样的比表面积影响较大,一般来看,热解温度升高焦样的比表面积增大;保持时间越长,焦样比表面积越大。热解条件对微孔范围内的孔径分布影响较大,对大孔范围内的孔径分布影响较小。吸附实验表明,生物质焦对二氧化硫和一氧化氮具有一定的吸附能力;生物质焦对二氧化硫的吸附能力比一氧化氮的好;生物质焦单独吸附一氧化氮时的效果不好,而当烟气中存在二氧化硫的时候,生物质焦对NO的吸附能力有所提高。烟气温度对吸附效果有影响,较低的烟气温度对吸附有利,烟气温度高于100℃以上时对SO2和NO的脱除不利。生物质焦的吸附效率不如活性炭。制焦条件对焦的吸附性能有影响,综合看来,最佳的制焦条件为:热解温度500℃-600℃、快速加热、保持时间10mins。对实验结果进行进一步分析发现。烟气温度升高会使气体分子的动能增大,引起气体分子挣脱,不利于吸附。生物质焦的吸附能力主要是由焦样的孔隙结构和表面化学性质决定的。焦样表面的碱性含氧官能团能促进氧化反应,对脱硫有益。一般地,焦样比表面积越大,其吸附能力越大。不过比表面积不是衡量吸附能力的唯一参数.生物质焦样的吸附能力还与生物质种类、表面含氧官能团和孔径分布有关。更多还原

【Abstract】 Sulfur dioxide and nitrogen oxide are the primary air pollutants from combustion resources, and it draws a wide attention around the world about how to control their emissions economically and efficiently. Currently, there have been many desulfurization and denitrification methods. Among them the activated carbon method is widely noticed because of its feasibility of reducing sulfur dioxide and nitrogen oxide simultaneously and of sorbent regeneration. But the high cost makes it difficult for activated carbon to meet the requirement of widely ustilization. So the researchers are looking for new sorbents with low cost and high adsorption efficiency. In order to use the biomass energy efficiently, we propose a new technology that combines the use of biomass energy and the use of the biomass products for the control of pollutants from coal combustion, in which the biomass char is used as a sorbent. In this thesis, the capacity of biomass char to adsorb sulfur dioxide and nitrogen oxide of flue gas are studied.In the present work, eight kinds of biomass fuels are employed. Different pyrolysis temperatures (400℃、500℃、600℃、850℃)、heating rates (fast、slow) and reaction times (10 minutes、20 minutes、30minutes) are taken to study the effects of the pyrolysis conditions on the char adsorption ability. In order to characterize the properties of the chars, Scanning Electron Microscopy (SEM) is used to observe the morphology, and Fourier Transform Infrared Spectrometer (FTIR) is used to get the surface chemical characteristics, and nitrogen adsorption method and mercury porosimetry are used to measure the special surface area and pore-size distribution. The adsorption experiments are carried out on a self-designed small-scale test facility to study the efficiencies of using biomass chars to adorb SO2 and NO speparately and simultaneously. In the experiments, the concentrations of the SO2 and NO are measured using a flue gas analyzer. Additionally, the adsorption capacities of biomass char and activated carbon are compared. At last the effects of some factors on the biomass char adsorption efficiency are discussed.The observation of Scanning Electron Microscopy shows that, after pyrolysis, the coarseness of biomass char surface is enhanced, and both the special surface area and the porosity of the char increase. There are adsorption peaks of silicon dioxide、oxalic acid root、carbonic acid root、hydroxy root、methyl、methylene on the FTIR curves. The carbonization degree of the char is enhanced and the surface function groups are reduced as the pyrolysis temperature increases.The nitrogen adsorption method is applied to measure the mesopores and micropores of the chars while the mercury porosimetry used to measure the macropores and part of mesopores. The results show that, the special surface area of the chars obtained by nitrogen adsotption varies from 0.1 m2/g to 400 m2/g, while those measured by mercury porosimetry vary relatively less from from 10 to 60 m2/g. The micropores of the chars distribute mainly in the range of 0.8-1.5nm and 1.8-3.5nm, and the mesopores and macropores distribute mainly in the range of 10-60nm and 60-600nm. The pyrolysis temperature affects the special surface area obviously. Commonly, the surface area increases as the temperature increases and as the pyrolysis time extends. The pyrolysis condition has a considerable effect on the micropore-size distribution while a relatilvey smaller effect on the macropore-size distribution.The adsorption experiments show that the biomass chars have a certain adsorption capacity for sulfur dioxide and nitrous oxide. The capability of the chars for sulfur dioxide adsorption is better than that for nitrous oxide. The adsorption efficency of nitrous oxide is low when there is only nitrous oxide in the flue gas but is improved when the sulfur dioxide also exists. The flue gas temperature has an effect on the adsorption efficiency. The adsorption efficiency is higher when the flue gas temperature is lower, but is lower when the temperature is above 100℃. Activated carbon has better adsorption capacity than biomass chars. Summarising the experimental results of this study, the best pyrolysis condition is fast pyrolysis at 500℃to 600℃with 10 minutes pyrolysis time.更多还原