流化床O2/CO2气氛对烟煤焦反应速率的影响研究王文康1,卜昌盛1,熊金琴1,王昕晔1,张居兵1,朴桂林1,张孝勇2

流化床O₂/CO₂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O₂/CO₂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O₂和CO的浓度,深入考察了O₂/CO₂取代O₂/N₂后,不同的床层温度(800～900 ℃)、O₂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:O₂/CO₂气氛下,煤焦反应速率随床层温度的升高、O₂浓度的升高和颗粒粒径的降低而增加; 煤焦燃烧反应由O₂扩散控制,气化反应由反应动力学控制; 相较于O₂/N₂气氛,低床温下,O₂/CO₂气氛下的O₂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O₂/CO₂气氛下O₂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.

Investigation on Reaction Rate of Bituminous Coal-Char Particlesin O2/CO2 Atmosphere in a Fluidized Bed

Oxy-fuel fluidized bed(FB)combustion is one of the promising technologies achieving the clean utilization of coal and nearly zero emission of CO₂ 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 O₂/CO₂ and O₂/N₂ atmospheres through continuously measuring the concentrations of O₂ and CO in the exit gas at the bed temperatures of 800～900 ℃,the O₂ 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,O₂ concentration and the decrease of the coal-char size in O₂/CO₂ atmosphere. Oxidation of coal-char is controlled by the diffusion of O₂,whereas gasification of coal-char is limited by the reaction kinetics. Compared with coal-char combustion in the O₂/N₂ atmosphere,the decreased diffusivity of O₂ in CO₂ is the main reason for the changed reaction rate of coal-char particle in O₂/CO₂ atmosphere at a low bed temperature. However,at a high bed temperature,in spite of the low diffusion rate of O₂,the effect of gasification on the coal-char reaction could not be ignored as consequence of the increased gasification rate.