烟气循环倍率对煤粉富氧燃烧影响数值模拟

Numerical simulation on influence of flue gas recirculation ratio on oxy-coal combustion

为了研究煤粉富氧燃烧方式下烟气循环倍率对燃烧和传热特性的影响,本文以某500k W燃烧测试炉为研究对象,采用数值模拟方法对空气燃烧以及不同循环倍率下的富氧燃烧进行了研究;采用化学渗透脱挥发分(CPD)模型模拟煤粉的脱挥发分过程,挥发分成分考虑为多种轻质气体,挥发分的燃烧采用详细化学反应机理,介质辐射特性模型均针对富氧燃烧进行了修正。研究结果表明:虽然富氧燃烧下二次风与一次风的动量比较空气燃烧下降了50%以上,但采用相同的旋流燃烧器仍可实现与空气燃烧相似的炉内流场特性;煤粉燃烧温度和着火位置均受循环倍率的影响,富氧燃烧下循环倍率为72%时,炉内平均温度分布以及着火位置与空气燃烧下较为接近,随着循环倍率增加,辐射传热量降低。

To study the effects of flue gas recirculation ratio on combustion and heat transfer characteristics in oxy-coal combustion, numerical investigation on air combustion and oxy-fuel combustion of pulverized coal was carried out in a 500 kW combustion test facility. Moreover, the chemical permeation devolatilization(CPD) model was used to describe the devolatilization behavior of pulverized coal. The volatile components are considered as a variety of light gases. The detailed reaction mechanism was applied for volatiles combustion, and the radiative property models were modified for oxy-fuel combustion. The results show that, although the momentum ratio of the secondary air to the primary air is reduced by more than 50% in oxy-fuel combustion, employing the same swirl burner can still obtain the in-furnace flow characteristics which is similar to the air combustion. Both the combustion temperature and the ignition position of the pulverized coal are affected by the circulation rate. In oxy-fuel combustion with recirculation ratio of 72%, the distribution of the average temperature in the furnace and the ignition position are similar to those in air combustion. As the increase of recirculation ratio, the radiative heat transfer decreases.