高海拔低气压条件下烟气辐射特性

Radiative properties of flue gas under high-altitude sub-atmospheric pressure

高原地区特殊的地理环境导致锅炉运行出现出力不足、排烟温度高等一系列问题。采用逐线法(Line-By-Linemethod, LBL),基于HITEMP2010光谱数据库(High-temperaturemolecular spectroscopic database),求解3组不同气压条件下(0.101 325、0.076 622和0.061 655 MPa)空气燃烧方式的烟气吸收系数和总发射率,分析了压力、温度和水蒸气与CO_(2)的摩尔比对烟气辐射特性的影响,改进了灰气体加权和(Weighted-Sum-of-Gray-Gases,WSGG)模型关联式,建立了适用于低气压条件下的WSGG模型参数。结果表明,压力的降低会减小烟气的总发射率,4种工况下压力从0.101 325 MPa下降到0.061 655 MPa时,总发射率随行程长度变化的最大差值分别为0.093 4、0.084 5、0.091 1和0.084 3。在小行程长度下,摩尔比越大,压力的变化对总发射率的影响越大,而大行程长度下则相反。温度的升高会减小烟气的总发射率,4种工况下,温度从1 000 K升到2 500 K时,总发射率随行程长度变化的最大差值分别为0.273 6、0.270 5、0.251 5和0.250 5。在小行程长度下,摩尔比越大,温度的变化对总发射率的影响越大,在大行程长度下则相反。摩尔比的增加会增大烟气的总发射率,4种工况下摩尔比从1增加到2时,总发射率随行程长度变化的最大差值分别为0.088 1、0.100 4、0.088 9和0.100 6。在小行程长度下,温度越高或压力越低,摩尔比变化对总发射率的影响越小,在大行程长度下则相反。改进后的WSGG模型在不同工况下烟气总发射率的最大相对误差为3.67%,相比现有基于常压条件下开发的WSGG模型外推到低压条件的误差有明显降低,表明改进后的WSGG模型更适用于低气压空气燃烧气氛。

The special geography of the plateau area leads to a series of problems in boiler operation.In this study,the absorption coefficients and total emissivity of flue gas were determined under different air pressures during air combustion using the Line-By-Line(LBL)method based on the HITEMP2010 database(High-temperature molecular spectroscopic database).The effects of pressure,temperature,and molar fraction(H_(2)O and CO_(2))on the radiative properties of flue gas were analyzed.An improved Weighted-Sum-of-Gray-Gases(WSGG)correlation,which relates the absorption coefficients to temperature and total pressure,was proposed.The results show that the reduced total pressure diminishes the total emissivity of flue gas.The maximum differences in total emissivity along the path lengths for the four working conditions with a pressure drop from 0.101325 to 0.061655 are 0.0934,0.0845,0.0911,and 0.0843,respectively.For a larger molar fraction,the effect of pressure on the total emissivity is greater for shorter path lengths but not for longer ones.Sim-ilarly,the higher temperature would reduce the total emissivity of flue gas.The maximum differences in total emissivity along the path lengths for the four working conditions with a temperature increase from 1000 K to 2500 K are 0.2736,0.2705,0.2515,and 0.2505,respectively.For a larger molar fraction,temperature has a greater effect on the total emissivity for shorter path lengths but not for longer ones.Furthermore,increasing the molar fraction enhances the total emissivity of flue gas.The maximum differences in total emissivity along the path lengths for the four working conditions with a molar fraction increase from 1 to 2 are 0.0881,0.1004,0.0889,and 0.1006,respectively.For a higher temperat-ure or lower pressure,the effect of molar fraction on the total emissivity is smaller for shorter path lengths but greater for longer ones.The maximum relative error of the improved WSGG model for the total emissivity of flue gas under different working conditions is 3.67%.It is a significant reduction in the error compared to that of the existing WSGG model.Therefore,the improved WSGG model is more accurate for air combustion atmosphere and sub-atmospheric pressure.