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循环流化床解耦燃烧（CFBDC）实现低氮氧化物（NOx）排放是可行的，这项技术在处理白酒糟（distilled spirit lees（DSL））的工业示范装置上已经得到了验证。低NOx排放被认为是DSL热解产物（包括焦炭，焦油和热解气体（py-gas））在立管燃烧器中再燃时共同还原NOx的结果。为理解CFBDC系统中NOx的还原机理，本研究通过实验室用沉降炉（DTR）模拟再燃条件下的生物质焦炭、焦油和焦炉煤气对NO的还原能力。 本论文在500℃下热解DSL制备测试用焦炭和焦油，热解气根据实验所得裂解气成分模拟配置。为确保NO被充分还原，大多实验设定试剂的总质量给料速度为0.15g/min。第4章首先研究了NO还原效率（ηe）随反应物进料速率、再燃化学计量比（SR）、反应温度、停留时间和初始烟气组成成分的变化关系。结果表明，在指定相同质量比条件下，焦炭比热解气更能抑制NO的产生。热解气中CO的存在抑制了均相NO还原反应，导致该试剂的ηe较低。由DSL制备的焦炭和焦油，高温和高的初始NO、CO浓度促进其对NO的还原。本章的主要结论是：通过热解产物再燃烧获得最高ηe的合适SR值为0.6-0.8。 基于上述结果，第5章评估和讨论了焦炭，焦油和热解气对NO还原的协同效应。NO还原试剂的总质量比一定时，结果对比表明，相比于其他工况，焦炭/热解气（二元试剂）能够实现最佳的协同NO还原效果，且还原效率随着热解气比例的增加而升高。当焦油比例降低至26％时，焦油/焦气或焦油/焦炭混合物才产生积极作用。此外，热解产物在NO还原过程中，焦炭与某些物质（如H2，CxHy）之间存在有效的相互作用，其协同效应与试剂中C，H元素与进料NO的摩尔比密切相关（CH/NO比）。 第6章进一步研究了来源于其他燃料如木屑（SD）和先锋（XF）褐煤的焦炭和焦油试剂的还原能力。在一定的还原剂质量比率下（0.15g/min），SD焦炭或XF褐煤焦由于灰分含量较低（含有催化物质），还原NO效率低于DSL焦炭，但SD焦油在三次测试中的ηe最高。值得注意的是，焦油总是表现出比焦炭更好的NO还原能力，因此更具吸引力。以苯酚、苯、乙酸、乙酸甲酯和庚烷等作为模型焦油化合物进行NO去除的试验，结果表明， 在NO还原方面，焦油中的苯酚组分作用显著。无论是生物质焦油还是煤焦油，含有至少一个芳香环（如苯酚，苯）的化合物组分，都是NO还原的主要贡献者。 综上，本研究的结果将对CFBDC系统处理富N燃料在运行方面具有重要指导意义。考虑到热解产生的焦油作为降低CFBDC中NOx排放的主导因素，建议进一步的研究集中于焦油的NO还原动力学分析，包括与其他成分的协同作用。另外，热解温度对试剂NO还原活性的影响也值得研究。;The technical feasibility of low-NOx emission in the so-called circulating fluidized-bed decoupling combustion (CFBDC) was previously verified in an industrial demonstration plant treating distilled spirit lees (DSL). The lowered NOx emission was believed to result from the combined actions of DSL pyrolysis products including char, tar, and pyrolysis gas (py-gas) upon reduction of NOx during their reburning in the riser combustor. In order to further understand the mechanism of NOx reduction mechanism in CFBDC system, this study is devoted to investigating the capabilities of biomass char, tar, and py?gas for NO reduction through experiments in a lab?scale drop-tube reactor (DTR) simulating their reburning conditions in CFBDC. In this thesis, the pyrolysis of DSL at 500 °C was conducted to produce the tested char and tar, while the py-gas was prepared from cylinder gases according to the analysis of experimental py-gas. To ensure sufficient reduction of NO, total mass feeding rate of reagents specified for most experiments was set at 0.15 g/min. The variations of NO reduction efficiency (ηe) with reagent feeding rate, reburning stoichiometric ratio (SR), reaction temperature, residence time, and initial flue gas composition were firstly investigated in Chapter 4. It was found that tar enabled the best NO reduction in comparison to char and py-gas at the same mass rate (specified). The presence of CO in py-gas inhibited the homogeneous NO reduction reactions to cause lower ηe by this reagent. For DSL-derived char and tar, their realized NO reduction reactions were promoted by high temperature and high initial NO and CO concentrations. The main conclusion of this chapter is that the suitable SR values for obtaining the highest ηe by reburning pyrolysis products were found to be 0.6 ? 0.8. Based on above results, the synergetic effects of such char, tar and py-gas reagents on NO reduction were evaluated and discussed in Chapter 5. The comparison on the basis of specified total mass rate for NO-reduction reagent indicated that the char/py-gas (binary reagent) enabled the best synergetic NO reduction than the others did, and the realized efficiency elevated with the increase in py?gas proportion. The tar/py-gas or tar/char mixture only caused a positive effect when tar proportion was necessarily lowered to about 26%. In addition, there existed effective interactions between char and some species in py?gas (i.e., H2, CxHy) during NO reduction by pyrolysis products, and the synergetic effects were closely related to the molar ratio of C, H elements in reagents to fed NO (CH/NO ratio). The NO reduction capabilities of char and tar reagents derived from other fuels such as sawdust (SD) and Xianfeng (XF) lignite were further investigated in Chapter 6. At the specified mass rate of reductant, say, 0.15 g/min, SD char or XF lignite char were less efficient than DSL char in reducing NO due to their lower content of ash (containing catalytic matters), whereas SD tar enabled highest ηe among three tested tars. Above all, tar, as an attractive reagent, always exhibits better NO reduction than char does. The tests of model tar compounds including phenol, benzene, acetic acid, methyl acetate and heptane for NO removal revealed that phenol plays an important role in enabling the good NO reduction for the SD tar. The major understanding from NO reduction by tar is that the compounds containing at least an aromatic ring (e.g. phenol, benzene) are the major contributor for reducing NO in either biomass tar or coal tar. In general, the results of this study promise to be significant in the operation of CFBDC system treating N-rich fuel. Considering the pyrolysis-generated tar as a dominant factor in lowering NOx emission in CFBDC, further studies are suggested to focus on kinetic analysis of the NO reduction by tars including the combined action of other constituents. Additionally, effect of pyrolysis temperature on NO reduction activity of reagents should be investigated.
|DO HAI SAM. 循环流化床解耦燃烧（CFBDC）过程低NOx排放机理研究[D]. 中国科学院大学,2018.|
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