典型尺寸燃煤颗粒富氧燃烧特性及燃烧本征动力学研究

Study on oxyfuel combustion behavior and the intrinsic kinetics of typically sized coal particles

利用微型流化床加热速度快、温度分布均匀以及气体近平推流等优势,在直径20 mm自动控温的微型流化床反应分析仪中研究了粒度分布为1.7~3.35 mm和0.12~0.23 mm两种典型尺寸燃煤颗粒在790~900℃温度范围内的富氧燃烧行为。通过快速响应过程质谱对燃烧产生的烟气进行实时监测,成功地识别和记录了粗颗粒燃烧过程中经历的挥发分燃烧和原位新生半焦燃烧两个主要阶段。挥发分析出速度最快,然后快速燃烧,而半焦燃烧速度较慢。相比之下,细颗粒燃烧的这两个阶段具有几乎相同的速率,因而相互耦合而难以区分。根据实验结果,挥发分析出和燃烧为快速反应,煤颗粒燃烧过程速率受原位新生半焦燃烧过程控制。进一步研究了挥发分和原位新生半焦燃烧动力学行为,获得其本征动力学的活化能分别为107.2和143.9 kJ/mol。

Oxyfuel combustion is a promising technology to facilitate carbon capture from combustion-generated flue gases.Circulating fluidized beds(CFBs), the major commercial-scale boilers, will play a significant role in the energy industry’s transition from today’s carbon-intensive to carbon neutral in the future. The types of boilers combust coals of wide screening particle sizes of 0~10 mm. The difference in coal particle size inevitably leads to a considerable variation in combustion characteristics, which has not yet been fully understood. In particular, little is known about the dynamic evolution behavior of combustion gas products and the intrinsic kinetics of the insitu produced nascent char particles when these typically sized coal particles are combusted in fluidized beds. For this reason, an advanced micro fluidized bed reaction analyzer(MFBRA), integrated with a fast-responding process mass spectrometry, was employed to investigate the oxyfuel combustion behavior of two typically sized coal particles(i.e., 1.7~3.35 mm and 0.12~0.23 mm), typical of those in dense region and dilute region in CFBs, at 790~900℃. The use of MFBRA enabled the successful detection and characterization of the dynamic combustion process-sequentially occurring devolatilization and combustions of the in-situ produced volatiles and the nascent char particles. The results demonstrated that the combustions of volatiles and nascent char particles can have similar or different rates depending on the coal particle size. The two major successively occurring dynamic processes were distinctively identified and characterized for the coarse particles but not for the fine particles, which were featured with similar reaction rates for the two processes. The combustion of coarse char particles was rate-controlled by kinetics at low temperatures and changed to interparticle diffusion control at high temperatures. The combustion kinetics of the volatiles and nascent char were analyzed, and the corresponding values of activation energy were107.2 and 143.9 k J/mol, respectively.