高浓度CO_2气氛下煤粉的燃烧及其孔隙特性

Pulverized Coal Combustion Under High CO_2 Environment and Its Porosity Characteristics

采用热力工况与实际煤粉炉相近的沉降炉,获取了不同环境气氛、不同燃烧温度下的煤焦试样并采用低温氮吸附仪测定了其吸附曲线。实验结果显示,相同的实验条件下,相同O2浓度的O2/CO2气氛下煤焦的燃尽率较低,各试样的孔比表面积和比孔容积均较小,在O2/CO2气氛下所取煤焦试样的分形维数均小于相同O2浓度的O2/N2气氛下所取煤焦试样的分维,表明大量高比热性CO2气体的存在不利于煤焦颗粒燃烧反应的进行及其孔隙结构的发展。同时,吸附等温线及其回线的形态表明,所取的试样具有完整且连续的孔结构体系,孔径范围小至分子级孔,大至无上限孔(相对而言)。研究结果为深入认识O2/CO2气氛下煤粉的孔隙结构与其燃烧特性的关系提供了基础。

In a drop tube furnace with the combustion conditions similar to those in actual pulverized-coal boiler furnace, coal char samples, partly burnt under different environments and temperatures, were prepared and analyzed with N2 adsorption analyzer at low temperature. The experimental results show that compared with in O2/N2 environments, the conversion of chars is always lower, specific surface area, pore volume and fractal dimension are also smaller in O2/CO2 environments for equivalent oxygen concentrations. It indicates that the presence of high CO2 concentration with larger specific heat is unfavorable to the pulverized coal combustion, and the formation and development of pores in char. Adsorption isotherms with hysteresis loops of char samples indicate that these samples consist of continuous and complete system of pores. The diameter of pores ranges from molecular scale to infinite upper limit （contrast to normal one）. Findings of present research might have important implications for better understanding the relationship between pore structure and combustion characteristic of pulverized coal in O2/CO2 environment.