O_2/CO_2气氛快速升温煤焦低温氮吸附等温线形态分析

Morphological Analysis of Low-temperature Nitrogen Adsorption Isothermal Curves of Coal Coke Undergoing a Quick Temperature Rise in an O_2/CO_2 Atmosphere

利用热力工况与实际煤粉炉相似的沉降炉实验装置,在快速升温条件下制备了两种燃烧气氛(O2/CO2和O2/N2)、不同O2浓度以及不同停留时间下的煤焦试样,采用AS-AP2020M型全自动比表面积及孔隙度分析仪测定了各煤焦试样的低温氮吸附等温线。分析表明,各不同条件下获取的煤焦试样的吸附等温线形态均为典型的Ⅱ型吸附等温线(即反S型),煤焦具有小至分子级的孔(孔径约0.86nm)大至无上限孔(相对)的较连续的完整的孔体系。吸附回线形态的分析可知,煤焦试样的孔隙可能包含大量不产生吸附回线的盲孔(一端封闭的圆筒孔、一端封闭的平行板状或劈尖状孔)以及部分的裂缝孔隙。结果表明,燃烧气氛的改变并未使得煤焦燃烧过程孔隙的形成与发展发生显著的变化,但与O2/N2气氛相比,在O2/CO2气氛下所取焦样的等温线与之存在着细微的差别,其表明不同条件下的焦样存在着不同的孔径分布。实验结果为进一步研究高浓度CO2气氛下煤粉的燃烧过程及其与常规燃烧模式的差异提供了一定的帮助。

By utilizing a sedimentation furnace test device with thermodynamic operating conditions similar to those of an actual pul-verized-coal boiler and under the condition of quickly rising temperatures,prepared were coal coke samples in two com-bustion atmospheres (O2/CO2 and O2/N2) ,with different oxygen concentrations and residence times. By using an AS-AP2020M type of full-automatic specific surface area and porosimeter,determined were the low-temperature nitrogen ad-sorption isothermal curves of various coal coke samples. The analytic results show that the shapes of adsorption isothermal curves obtained from the coal coke samples under various conditions are all typical adsorption isothermal curves of Type Ⅱ (reversed S shape).The coal coke has a relatively continuous and integral pore system with pore diameters ranging from the smallest molecular grade (pore diameter about 0.86 ran) to the largest without an upper limit (relative). It can be seen from an analysis of the shapes of the adsorption loop curves that the pore of the coal coke samples may contain many blind pores (cylindrical holes,and parallel plate-shaped or cut-pointed ones with one closed end) that produce no adsorp-tion loop curves,including a portion of cracking pores. It has been found that a change of combustion atmosphere causes no marked changes in the formation and development of pores during the combustion of coal coke. However,compared with the isothermal curves obtained from the coal coke samples in the O2/N2 atmosphere,those obtained in the O2/CO2 atmo-sphere feature a slight difference,indicating a different pore diameter distribution of the coal coke samples in various con-ditions. The test results have provided a certain basis for a further investigation of the combustion process of pulverized coal in a high concentration CO2 atmosphere and its difference from a conventional combustion mode.