劣质煤种对1000MW旋流对冲锅炉燃烧性能的影响

Influence of low quality coal on the combustion performance in a 1000 MW swirl opposed firing boiler

旋流对冲燃烧锅炉在燃用劣质煤种时,由于劣质煤着火困难,会造成主燃区温度较低,引起炉内燃烧不稳定,并且水冷壁经常发生高温腐蚀和结渣,上部对流受热面超温,飞灰含碳量也增加,锅炉热效率明显降低,是目前电站锅炉运行面临的一大难题。针对某1000 MW旋流对冲燃烧锅炉,采用CFD方法研究了锅炉燃用劣质煤种时炉内燃烧组织的分布特性,并将结果与设计煤种进行了对比分析。结果表明:与设计煤种相比,劣质煤灰分高,热值低,原燃烧器的分级配风方式不利于劣质煤粉及时着火,燃点推迟,炉膛水平截面温度分布不均匀,四周水冷壁中心附近出现高温区和高浓度CO,炉膛中心高温区减小,火焰中心上移,因此对流受热面附近出现高温区域,这些会导致水冷壁高温腐蚀,对流受热面超温问题发生,同时出口烟温也会增加,即锅炉效率降低。另外,由于分级燃烧组织的不合理,炉膛出口NO x生成量也明显增加。在实际运行中,可以采用混煤掺烧的方式,改善劣质煤种的燃烧特性,从而提高锅炉燃烧稳定性;其次,可以对原旋流燃烧器进行改造优化,如适当减小一次风速,或者在水冷壁中心增设墙式风,保证劣质煤粉有足够的时间预热并能够及时与二次风混合,稳定着火,提高锅炉燃用劣质煤种的能力。

When the low quality coal is used in a swirl opposed firing boiler,it is difficult to ignite in time and burn out,which causes the temperature of the main combustion zone to be low.The unstable combustion of the furnace will lead to the high temperature corrosion and slagging in the water wall,and the overheating problems on the upper convection heating surface.the carbon content of fly ash is also greatly increased,thus the thermal efficiency of the boiler is significantly reduced.This is a major problem facing the operation of the power plant boilers.For a 1000MW opposed firing boiler,the combustion performance and the distribution of the characteristic parameters was studied by numerical simulation method when it was burned inferior coal,and the results were compared with the designed coal,so as to provide some basis for improving the coal adaptability of the boiler.The results show that,compared with the designed coal,the ash content of inferior coal is higher and the calorific value is lower.The classified air distribution mode of the original burner is not conducive ignited in time and maintain the stable combustion,and the fire point is postponed and the temperature distribution of the horizontal section of in the furnace is uneven.The high temperature area appears near the water wall.The large area of high concentration CO generates near the center of the water-cooled walls,and the high temperature zone in the furnace center also decreases for the incomplete combustion and the temperature of the convective heating surface rises up.That is,the flame center is close to the burnout zone,which is easy to cause the high temperature corrosion and slagging in the water-cooled wall,and the overheating of the convective heating surface.The fume temperature and carbon content in fly ash at the outlet also increases,that is,the boiler efficiency will decrease.In addition,due to the irrationality of the staged combustion organization,the production of NO x at the furnace outlet is also significantly increased.In the actual industrial application,the quality of the burning coal should be blent with the designed coal to improve the combustion characteristics of the low quality coal and ensure the combustion stability of the boiler.Also,the original swirl burner should be optimized and reformed,and the mixing of primary air and secondary air should be strengthened in advance,and the primary air velocity is reduced appropriately or the wall wind system is added near the water-cooled wall to ensure pulverized coal ignition in time and improve the ability of the boiler to burn the low quality coal.