碗式配风对燃烧效率与NOx质量浓度的影响

对600 MW超临界前后墙对冲燃烧锅炉在均等配风和碗式配风下的燃烧进行数值模拟，分析不同偏差程度碗式配风对炉内颗粒质量浓度场、CO体积分数场、炉膛温度、NO_x生成的影响，并与试验结果进行对比. 模拟结果表明，燃烧器碗式配风改善了炉内宽度方向上的风、煤混合过程，减小了CO体积分数和煤粉颗粒质量浓度偏差，降低了炉膛出口烟气中CO的平均体积分数和飞灰中碳的质量分数，从而有效提高了前后墙对冲燃烧锅炉的燃烧效率. 燃烧器碗式配风对炉膛出口烟气中NO_x的平均质量浓度有不利影响，但是当碗式配风风量偏差不大于20%时，NO_x平均质量浓度变化不大于3.5%. 综合燃烧器碗式配风对水平截面CO分布特征和炉膛出口烟气中NO_x的平均质量浓度的影响，在燃烧常用煤种的条件下，碗式配风的风量偏差宜控制在20%以内. 炉膛出口烟气中CO的平均体积分数、飞灰中碳的质量分数、NO_x平均质量浓度的模拟值与热态试验值变化趋势一致. 在实际应用中碗式配风对CO平均体积分数的降低效果更加显著，当碗式配风的风量偏差达到20%时，省煤器出口烟气中CO的平均体积分数降低幅度达95%.

Effect of bowl-shaped secondary air distribution on combustion efficiency and NOx mass concentration

The combustion process in a 600 MW supercritical opposite-wall-firing boiler under the conditions of equal and bowl-shaped secondary air distribution (BSAD) was numerically simulated. The influence of varying secondary air distribution deviation on the particle mass concentration field, CO volume fraction field, furnace temperature and NO_x generation was analyzed. The calculated results were compared with experimental data. The simulation results showed that BSAD enhanced the mixing between pulverized coal and air, decreased the bias of average CO volume fraction and particle mass concentration along the furnace width, reduced the average CO volume fraction in flue gas, carbon mass fraction in fly ash at the furnace exit, and improved the combustion efficiency of opposite-wall-firing boiler. BSAD did harm to the average NO_x mass concentration in flue gas at the furnace exit, however, the NO_x mass concentration varied within 3.5% when the deviation of the secondary air distribution was less than 20%. By combining the effects of BSAD on horizontal CO volume fraction distribution and average NO_x mass concentration in flue gas at the furnace exit, the appropriate deviation of BSAD for the boiler is recommended to be 20% when the boiler utilizes frequently-fired coal. The variation trend of numerical results of average CO volume fraction in flue gas, carbon mass fraction in fly ash, average NO_x mass concentration at the furnace exit is consistent with the in-situ experimental results. In practical operation, the effect of BSAD on declining average CO volume fraction is more significant, the reduction of average CO volume fraction at the economizer exit reaches 95% when the deviation of secondary air distribution equals to 20%.