【作者】 黄晓宏；

【导师】 柳朝晖； 陈胜；

【作者基本信息】 华中科技大学 ， 热能工程， 2013， 博士

【摘要】 富氧燃烧技术作为一项可以实现大规模CO₂富集的新型燃烧技术，近十年来受到了业内人士的广泛关注。由于实验系统的差异，富氧燃烧技术独具的高CO₂气氛对煤粉燃烧过程的影响及作用机理仍然没有得到一致的结论。本文借助自行搭建的平面火焰携带流反应器，对煤粉在接近真实炉膛的模拟烟气中的脱挥发分、着火及燃尽过程展开了详细的实验研究。本文首先在平面火焰携带流反应器中开展了煤粉的脱挥发分实验，研究了煤粉在富氧燃烧和常规空气燃烧条件下的脱挥发分特性和所制备煤焦的物理化学特性及反应性。实验结果表明：富氧燃烧气氛下高浓度CO₂的存在会抑制高挥发分煤（褐煤和烟煤）的挥发分释放，但会导致低挥发分煤脱挥发分产率的增加。同时，对比CO₂焦和N₂焦的物理结构和化学结构发现，高挥发分煤焦的比表面积增加，而低挥发分煤焦的比表面积降低。CO₂焦表面化学结构的活性均要高于N₂焦。但相比于化学结构，物理结构对煤焦表观反应性起主要作用。继而结合FF-EFR和高速CCD摄像机研究了煤粉在富氧燃烧和常规空气燃烧条件下着火和挥发分燃尽特性，着重对煤粉的着火延迟，着火稳定性和挥发分燃尽时间进行了探讨。实验结果表明：着火延迟时间反比于YO₂,sn，n约为0.15⁰.2。高浓度CO₂的存在会导致高挥发分煤粉着火延迟增加和着火稳定性降低。但与之相反，可以改善低挥发分无烟煤的着火延迟和着火稳定性。同时，高浓度CO₂的存在会导致高挥发分煤粉的脱挥发分和挥发分燃尽时间延长。在FF-EFR上结合采用沿程急冷颗粒采样技术，研究了中美典型动力煤在O₂/CO₂和O₂/N₂气氛下的燃尽特性，并根据实验数据求解了其基于煤焦氧化反应的表观反应动力学参数和基于四步反应的详细反应动力学参数。研究结果表明：高氧浓度条件下，高浓度CO₂对煤焦燃尽的抑制作用大于气化反应对煤焦燃尽的促进作用。降低环境氧浓度可以提高CO₂气化反应对煤焦燃尽的贡献。低氧浓度条件下，高浓度CO₂气化反应对煤焦燃尽有着明显的促进作用。CO₂气化反应对无烟煤的燃尽作用不明显。煤焦与CO₂的气化反应所产生的煤焦表面对O的化学吸附，进而导致了煤粉在富氧燃烧条件下的氧元素释放速率减慢。煤粉燃尽过程实际上是原始无定形碳的消耗与新无定形碳的生成相竞争的过程。在脱挥发分阶段，大芳香环系统（微晶石墨）保持稳定，脂肪链的芳构化反应导致了小芳香环系统的生成（无定形碳）。在焦炭燃尽的早期和后期，煤焦氧化反应的发生使得无定形碳的生成和消耗分别占主要作用。同时，研究发现在高转化率条件下由于灰壳的屏蔽效应，仍然有一定量的无定形碳和微晶石墨残余在总灰中。最后，通过动力学求解，为相应煤种的数值模拟研究和工业应用提供了表观反应动力学和详细反应动力学数据。更多还原

【Abstract】 Oxy-fuel combustion technology （also named O₂/CO₂combustion technology） ofpulverized coal has received considerable attention as one of the potential approaches toachieve a sequestration ready CO₂gas stream from coal fired power plants. Due to thedifferenced in the experamental conditions, it was inconsistent that the effects and actionmechanisms of high content CO₂on the combustion process of pulverized coal. Thedevolatilization, ignition and burnout processes of pulverized coal were investigated indetail under the simulated flue gas, which was close to the industrial furnace and wasprovided by the flat-flame assisted entrained flow reactor.A flat-flame assisted entrained flow reactor was used to conduct the devolatilizationexperiment. The chars were prepared under oxy-fuel and air combustion conditions. Theapparent volatile yields, the physical-chemical properties and reactivites were studied. Theresults indicate that the high content CO₂inhibits the volatile release of high volatile coal（lignite and bituminous coal） and increases the apparent volatile yield of low volatile coal（anthracite coal）. The high content CO₂also increases the specific surface area of highvolatile coal and decreases the specific surface area of low volatile coal. Meanwhile, theactivity of chemical structrues of char-CO₂is higher than that of char-N₂. Compared to thechemical characteristics, the physical characteristics of char play a major role on theapparent reactivity.The ignition and devolatilization behaviors of pulverized coals under oxy-fuel and aircombustion conditions were investigated using the high speed camera. The ignition delaytime, ignition stability and delay of devolatilization were analyzed. The results indicatedthat the ignition delay time is inversely proportional to YO₂,sn，n is0.15⁰.2. The present ofhigh content CO₂lead to the increase of ignition delay time and ignition stability of highvolatile coal. To the contrary, the present of high content CO₂lead to the decrease ofignition delay time and ignition stability of low volatile coal. Meanwhile, the high contentCO₂lead the delay of devolatilization procedure.The burnout behaviors of selected Chinese and U.S. typical power coals under O₂/CO₂and O₂/N₂atmospheres were investigated in the flat-flame assisted entrained flow reactor.And the reaction kinetic parameters based on the char oxidation reaction （C+0.5O₂→CO）and four steps detail reactions were respectively solved from the burnout curves. The results indicated that the suppression effect of high content CO₂on char burnout is morethan promotion effect of CO₂gasificaition reaction on char consumption at the high oxygencondition. The contribution of CO₂gasificaition reaction on char consumption can beenhanced through reducing the oxygen concentration. At the low oxygen conditions, thepromotion effect of CO₂gasificaition reaction on char consumption is obvious. But thepromotion effect cann’t be observed on JC anthracite coal. The oxygen atoms chemicallyadsorbedon char surface, resulted by the char-CO₂gasification reaction, leads the reduce ofrelease rate of oxygen element. The coal burnout process was found to be the competitiveprocess between elimination of the original amorphous mass and formation of newamorphous materials. At the stage of pyrolysis, the large aromatic ring system （microcrystalgraphite） keep stable, and the aromatization of aliphatic chain caused the increase of smallaromatic ring system （amorphous carbon）. At the early and late stage of char burnout, thegeneration and consumption of amorphous carbon respectively play a dominant rolebecause of oxidation reaction. This finding is important for analyzing the change of charreactivity during char burnout.Finally, the reaction kinetic data were collected, which can be used to build a databaseand incorporated into a computational fluid dynamics model for subsequent design andscale-up purposes.更多还原