流化床O_2/CO_2气氛对烟煤焦反应速率的影响研究

Investigation on Reaction Rate of Bituminous Coal-Char Particles in O_2/CO_2 Atmosphere in a Fluidized Bed

流化床O_2/CO_2燃烧是实现煤炭清洁利用及近零碳排放的有效技术之一.为进一步探究工业流化床O_2/CO_2燃烧条件下的煤颗粒燃烧机制,本研究在小型流化床试验台上,通过在线测量流化床出口烟气中O_2和CO的浓度,深入考察了O_2/CO_2取代O_2/N2后,不同的床层温度(800~900℃)、O_2浓度(4%~10%)及颗粒粒径(2~8 mm)下的烟煤焦燃烧特性.实验结果表明:O_2/CO_2气氛下,煤焦反应速率随床层温度的升高、O_2浓度的升高和颗粒粒径的降低而增加;煤焦燃烧反应由O_2扩散控制,气化反应由反应动力学控制;相较于O_2/N2气氛,低床温下,O_2/CO_2气氛下的O_2扩散速率降低是煤焦反应速率改变的主要原因;高床温下,除O_2/CO_2气氛下O_2的扩散速率降低外,煤焦气化反应对煤焦反应速率的影响同样不可忽略.

Oxy-fuel fluidized bed( FB) combustion is one of the promising technologies achieving the clean utilization of coal and nearly zero emission of CO_2 from coal fired power plants. To obtain the oxy-fuel combustion characteristics of coal particles in the industry FB conditions,experimental study of combustion of bituminous coal particles is conducted in a bench-scale FB in O_2/CO_2 and O_2/N2 atmospheres through continuously measuring the concentrations of O_2 and CO in the exit gas at the bed temperatures of 800 ~ 900 ℃,the O_2 concentrations of 4% ~ 10% and the coal particle sizes of 2-8 mm.Results indicate that the combustion rate of bituminous coal-char particle increases with the increase of bed temperature,O_2 concentration and the decrease of the coal-char size in O_2/CO_2 atmosphere. Oxidation of coal-char is controlled by the diffusion of O_2,whereas gasification of coal-char is limited by the reaction kinetics. Compared with coal-char combustion in the O_2/N2 atmosphere,the decreased diffusivity of O_2 in CO_2 is the main reason for the changed reaction rate of coal-char particle in O_2/CO_2 atmosphere at a low bed temperature. However,at a high bed temperature,in spite of the low diffusion rate of O_2,the effect of gasification on the coal-char reaction could not be ignored as consequence of the increased gasification rate.