流化床富氧燃烧湿烟气循环体系下的煤颗粒燃烧机理研究

Oxy-fuel fluidized bed (FB) combustion is considered one of the promising ways to control CO2 emission from the coal-fired power plants. Wet-recycle oxy-fuel combustion (O2/CO2/H2O) shows higher efficiency of the power plant and lower emission of pollutants than that of dry-recycle. The steam concentration in the oxy-fuel combustion is significantly high, which would directly affect the heat capacity of mixture gases, the diffusivity of O2 and cause the H2O gasification reaction. However, the mechanisms of the effect of steam on the coal combustion in O2/CO2/H2O atmosphere have not been revealed. To this end, tools for experiment and modeling will be performed in this project. Experimental tests of wet-recycle oxy-fuel combustion of typical Chinese coal particles will be carried out in a transparent and electrically heated FB and a thermogravimetric analyzer (TGA) obtaining the combustion characteristics when switching from air to oxy-combustion, and the reaction kinetics of reactions of char-O2, char-CO2 and char-H2O. A particle scale coal combustion model will be developed to study the effect of H2O on the combustion characteristics as a consequence of the changed heat capacity of mixture gases and diffusivity of O2, and study the relative contribution of carbon in the char consumed by H2O gasification under O2/CO2/H2O atmosphere in FBs. The accuracy of the model is validated by comparing the predicted results with the measured. In addition, the cooperation and competition of char-O2 reaction, char-H2O reaction and char-CO2 reaction will be quantitatively examined by means of the validated model. This project will provide the theoretical guidance and scientific basis for the developing of the technology of oxy-fuel FB combustion.

流化床富氧燃烧是极具发展与运用前景的CO2捕集技术之一。流化床湿烟气循环富氧燃烧（O2/CO2/H2O）方式优于干烟气循环富氧燃烧，但湿烟气循环条件下高水蒸汽浓度对煤颗粒燃烧的影响规律及影响机理尚未揭示。为此，本项目将以可视化流化床燃烧实验系统和自制热天平为实验平台，探究O2/CO2/H2O气氛下我国典型煤颗粒的燃烧特性，揭示煤焦-O2反应、煤焦-H2O反应和煤焦-CO2反应动力学及其交互影响机理；同时建立颗粒尺度的流化床煤颗粒O2/CO2/H2O燃烧模型，基于详实的实验数据验证并改进模型，通过O2/CO2/H2O气氛下煤颗粒的燃烧数值实验，定量揭示高H2O浓度下O2扩散速率的改变、比热容的改变、煤焦-H2O反应对煤颗粒燃烧的影响机制，探明煤焦-O2反应、煤焦-H2O反应和煤焦-CO2反应之间协同与竞争机制。通过本项目的研究工作为流化床富氧燃烧技术的发展提供理论指导和科学依据。

流化床富氧燃烧是极具发展与运用前景的CO2捕集技术之一。流化床湿烟气循环富氧燃烧（O2/CO2/H2O）方式优于干烟气循环富氧燃烧，但湿烟气循环条件下高水蒸汽浓度对煤颗粒燃烧的影响规律及影响机理尚未揭示。为此，本项目采用实验研究和数值计算研究相结合的方法，从探究富氧气氛下煤颗粒反应特性出发，提取化学反应动力学参数和宏观燃烧特性，至建立燃烧模型来揭示富氧气氛下煤颗粒的燃烧机制，依次开展研究工作。结果显示： O2/CO2/H2O气氛下H2O分子优先吸附于煤焦表面活性位点，O2分子次之，而CO2分子相对滞后，建立了O2、CO2、H2O混合气氛下煤焦反应速率L-H动力学方程，方程计算结果与实验值良好吻合；O2/CO2/H2O气氛下Char-CO2和Char-H2¬O反应的发生在提高反应速率的同时降低了燃烧温度；煤焦燃尽时间、峰值温度均随H2O和CO2浓度的升高而降低；且H2O对燃烧特性的影响较CO2更显著；Char-O2氧化反应仍是煤焦碳消耗量的主体，随着H2O浓度的提高，Char-H2O反应消耗碳占颗粒碳含量的比例上升，当H2O浓度达到30%时，Char-H2O所消耗碳量达颗粒碳含量的14%，而Char-CO2反应所消耗碳量占比相对较小。