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煤和生物质焦油还原NO研究
YUTTHASIN BUNMAN
Thesis Advisor许光文
2018-01
Degree Grantor中国科学院大学
Degree Name硕士
Degree Discipline化学工程
Keyword生物质油,煤焦油,模型焦油组分,再燃,脱硝反应
Abstract

燃料燃烧过程中生成的氮氧化物(NOx)作为主要大气污染物之一,造成多种环境污染问题如酸雨、高地面臭氧浓度、光化学烟雾等,并对人体健康造成诸多不良影响。在当今高能耗背景下保持友好型环境,减少NOx排放已成为全球重点关注的问题。因此,本论文通过在实验室规模下降管反应器中利用模型焦油吸收NO,评估热解焦油脱硝的反应特征及性能。本文首先研究了不同热解焦炭和焦油的脱硝性能,并与之前工作中相似条件下利用白酒糟 (DSL)热解焦油脱硝的实验结果进行了对比。化学计量比(SR)和温度被认为是脱硝的关键变量。焦炭和焦油都具有相当大的脱硝能力,且它们脱硝的效率随着温度从800到1000℃升高而升高。相同条件下,锯末(SD)热解焦油相较于其他被测焦油还原剂呈现最高的脱硝效率,在相同质量进料速率(0.15 g/ min)下,焦油相较于焦炭呈现更高的脱硝效率。另外,最大脱硝效率在化学计量比为0.6-0.9间得到,与循环流化床解耦燃烧系统下得到的最优化学计量比相似。进一步评估使用不同焦油并给出了焦油中各组分对其脱硝性能的影响。基本的模型组分如苯、苯酚、脂肪族、酸和酯被分别用来脱硝,可一定程度上揭示每种被测组分对脱硝性能的贡献。在同样的质量进料速率(0.15 g/ min)下,通过测试这五种焦油组分得出了苯酚相较于其他组分具有最高的脱硝能力。因此,苯酚在锯末(SD)热解焦油与白酒糟 (DSL)热解焦油脱硝过程中发挥主要作用,说明生物质热解油脱硝的主要有效组分为苯酚,而煤焦油中脱硝的主要有效组分为芳香族和脂肪族化合物。这解释了为什么生物质焦油的脱硝效率显著高于煤焦油。考虑到焦油中各组分的脱硝协同作用,后续有必要引入多组分进行脱硝测试探索其协同机理。此外,还揭示了利用焦油再燃烧脱硝过程的主要参数的影响,包括化学计量比(SR)、反应温度、停留时间(t)和初始NO浓度。实验结果表明,所有参数对焦油脱硝效率的变化都有显著的影响。随着化学计量比(SR)从0.4 增长到1.3,SD焦油和先锋 (XF) 煤焦油的脱硝效率先增加后减小,最大脱硫效率在化学计量比为0.6-0.7间获得。这些说明供氧量在NO转化过程中发挥关键作用。在富油(缺氧)条件下(SR= 0.6),脱硝效率随着温度从800到1000℃增大而显著增加,这说明对于被测还原剂,高温有助于提高脱硝效率。同时,反应时间越长,还原剂与NO反应更充分,从而提高了还原效率。此外,在再燃烧过程中初始NO浓度的增加会一定程度上增加NO和还原剂的接触,从而提高脱硝效率。;Nitrogen oxide (NOx), as one of the major serious atmospheric pollutants emitting from fuel combustion, causes harmful environmental pollutions including the acid rain, photochemical smog and many others. It impacts also human health. The reduction of NOx emission becomes thus an important subject of preserving global environment. This thesis mainly investigates the characteristics of NO reduction by pyrolysis tar in a lab-scale drop-tube reactor to deepen the understanding of the NO reduction by pyrolysis tar. The NO reduction capabilities of pyrolysis chars and tars of Sawdust (SD) and Xianfeng (XF) coal were firstly investigated and compared with the results realized by tar of Distilled Spirit Lees (DSL) in our previous work under the similar conditions. The stoichiometry ratio (SR) and temperature are considered as the key factors affecting the NO reduction by tar as well char which both showed considerable capability in reducing NO. Their realized NO reduction efficiencies increased with elevating temperature from 800oC to 1000oC. Under the similar conditions, Sawdust tar (SD tar) exhibited the best NO reduction efficiency among other tested agents. Furthermore, tars exhibited the higher NO reduction efficiencies than those realized by char under the same mass feeding rate (0.15 g/min) of reagent. Also, the maximal reduction efficiency was obtained at SR values of 0.6 - 0.9, which was similar to the optimal SR obtained for the circulating fluidized bed decoupling combustion (CFBDC) system. The NO reductions by major tar components were further evaluated to figure out their contributions to the capability of NO reduction by a tar. The used model compounds included benzene, phenol, aliphatic, acid and ester. Testing their NO reductions revealed that phenol enabled the best NO reduction capability among all tested model compounds at the same mass feeding rate of reagent (0.15 g/min). Therefore, phenol plays an important role to the NO reduction capabilities of both SD tar and DSL tar, indicating that the major contributor for reducing NO in biomass tar is phenols, while in coal tar this becomes aromatic or aliphatic compounds. Also because of this, biomass tar allowed the higher NO reduction efficiency than coal tar did. Nonetheless, more studies are needed to clarify the potential synergistic effects of tar components on NO reduction.In addition, the work examined the influences of major parameters of reburning process including the stoichiometry ratio (SR), reaction temperature, residence time (t) and initial NO concentration on the NO reduction efficiency by tar. All tested parameters significantly influenced the NO reduction efficiency by tar. With increasing the SR from 0.4 to 1.3, the realized NO reduction efficiency for both SD tar and XF coal tar first increased and then decreased, and the maximal NO reduction efficiency appeared at SRs of 0.6 - 0.7. This verified that the amount of O2 fed to the system plays an important role in NO conversion. Under the fuel-rich condition such as at SR=0.6, the realized NO reduction efficiency of tar obviously increased with elevating temperature in 800-1000oC, indicating that a higher temperature is beneficial to the NO reduction efficiency at this kind of SRs. Also, the longer reaction time enhanced the reactions between reductant and NO to improve the NO reduction efficiency. Moreover, the increase of initial NO concentration in reburning process was found to facilitate the contact of NO with reductant, thus raising the realized NO reduction efficiency

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26928
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
YUTTHASIN BUNMAN. 煤和生物质焦油还原NO研究[D]. 中国科学院大学,2018.
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