高温水蒸气氛围中煤燃烧特性研究
Study on Combustion Characteristics of Coals in High Temperature Water Vapor Atmospheres

针对煤燃烧过程中产生大量NOx的问题,提出了在燃烧系统中加入高温水蒸气来实现低氮燃烧的方案,并对此进行了热力学计算和实验研究。根据标准摩尔反应吉布斯自由能变、标准摩尔反应焓和平衡常数,理论计算了加入高温水蒸气后煤的挥发分燃烧过程中各反应发生的可能性和限度。反应路径推测的结果表明:高温水蒸气氛围中,在煤燃烧的温度区间内可能进行N元素转化为N2的反应。利用HSC Chemistry软件计算了过量空气系数不同时,在系统中加入不同含量的高温水蒸气后的平衡态组分。热力学计算结果表明:当过量空气系数在0.6～0.8、温度在700～800℃时,向燃烧体系中加入高温水蒸气可以抑制NOx生成;高温水蒸气的含量增加时,NOx减少率增加。利用煤粉固定床燃烧实验系统进行了在水蒸气和空气氛围中煤粉的燃烧特性实验。实验结果表明:加入高温水蒸气抑制了NOx的生成,且优于计算结果;NOx减少率与水蒸气体积分数呈现非线性关系。该研究可为煤的低氮燃烧提供经济高效的参考方案。
A scheme of adding high temperature water vapor to the combustion system to achieve low？？nitrogen combustion is proposed to reduce NOx production during coal combustion, and its thermodynamic calculation and experimental research are carried out. Firstly, the possibility and limitation of the reactions in the volatile combustion process of coal after adding high temperature water vapor are examined by theoretical calculation based on the standard molar reaction Gibbs free energy change, the standard molar enthalpy and the equilibrium constant. Results of reaction path speculation show that in the high temperature water vapor atmosphere, the reactions of converting N element to N2 occur in the temperature range of coal combustion. Secondly, in reactions with various excess air coefficients, the equilibrium components after adding different concentrations of high temperature water vapor are calculated using the software HSC Chemistry. Results of the thermodynamic calculation show that the reaction of NOx precursor to N2 happens in a wide temperature range: when the temperature ranges from 700 to 800 and excess air coefficient lies between 0.6 and 0.8, the formation of NOx significantly reduces by adding high temperature water vapor; Reduction rate of NOx increases with the concentration of high temperature water vapor increasing. Eventually, the combustion characteristics of pulverized coal in water vapor and air atmosphere are tested in a pulverized coal fixed bed combustion experiment system. It shows that the formation of NOx is inhibited by adding high temperature water vapor and the effect is better that the result of the thermodynamic calculation, and the NOx reduction rate has a nonlinear relation with the water vapor concentration and the temperature. This study may provide an economical and efficient reference solution to low NOx combustion of coal