煤种性质对煤粉工业锅炉结焦的影响

Influence of coal properties on coking of pulverized coal industrial boilers

燃煤锅炉内结焦会对锅炉运行的安全性和经济性造成极大损害,因而分析影响燃煤锅炉结焦的因素,进而有效预防燃煤锅炉结焦至关重要。在实际应用中,针对影响燃煤锅炉结焦的不同因素,可采取不同的预防措施。研究发现煤的灰熔融性温度、煤粉颗粒大小、锅炉燃烧气氛、一二次风动力场、锅炉截面热负荷和锅炉热负荷等都会影响燃煤锅炉结焦。为了解决某地区煤粉工业锅炉预燃室、炉膛、对流受热面大面积燃烧结焦问题,笔者结合燃煤锅炉燃烧结焦的机理,先后采取调整燃烧气氛、增大二次风刚性、减小煤粉颗粒粒径、更换孙家岔煤粉等措施对不同条件下的结焦现象进行对比分析,发现煤种、煤粉粒径大小是影响某地区煤粉工业锅炉燃烧结焦的因素。通过SEM-EDS(扫描电镜和能谱分析)对锅炉焦块进行微观形貌与元素组成分析,现场取样锅炉现用煤粉和孙家岔煤粉进行煤质及灰成分对比分析,并根据灰成分进行结渣性判别指标计算,结果表明锅炉燃烧现用煤种灰熔融性温度较低,煤灰软化温度Ts为1 170℃,小于1 200℃,为易熔煤,容易结渣,属于典型的易结焦煤种;结渣性判别指标计算结果显示,4项指标评价为"严重",1项指标评价为"中等",结渣性严重。综合分析认为:锅炉燃烧煤种发生改变,煤的灰熔融温度较低是影响某地区煤粉工业锅炉燃烧结焦的最本质因素。为进一步解决现场实际问题,采取破坏煤灰中酸碱平衡,提升煤的灰熔融温度,配合调节煤粉粒径等措施,如对锅炉现用煤种掺混5%的石英,提高煤灰中Si O2含量,掺混后煤粉的灰熔融温度达到1 280℃,提高了110℃;调大煤粉磨机频率,从19 Hz增大到22 Hz,煤粉粒度(200目,0.075 mm)过筛率从70%增大到85%。经过上述调整后,锅炉运行平稳,结焦状况显著改善,燃烧调整措施取得了较好的效果。

Coking in coal-fired boilers will cause great harm to the safety and economy of boiler operation.Therefore,it is important to analyze the factors affecting coking of coal-fired boilers and effectively prevent coking in coal-fired boiler. In practical application,different preventive measures can be taken for different factors affecting coking of coal-fired boiler.It is found that the melting temperature of coal ash,particle size of coal,combustion atmosphere of boilers,primary and secondary air force field,thermal loads of boiler section and boilers are the factors that affect the coking of coal-fired boilers. In order to solve the problem of large area combustion coking in precombustion chamber,furnace and convection heating surface in a specific pulverized coal boiler,based on combustion coking mechanism of coalfired boilers,the measures of by adjusting combustion atmosphere,increasing secondary air rigidity,reducing the pulverized coal particle size,replacing the pulverized coal were taken to analyze coking phenomenon under different conditions. The conclusion is that the types of coal and the particle size are the factors affecting the combustion coking of this specific pulverized coal boiler.The micro morphology and element composition of the coking block as well as the composition of different coals were analyzed by SEM-EDS,the coal quality and ash composition between the coal powder currently used in the on-site sampling boiler and Sunjiacha coal powder were compared and analyzed,and the slagging discrimination index was calculated according to the ash composition.The melting temperature of coal ash used in the boiler is relatively low.The softening temperature Ts is 1 170 ℃,less than 1 200 ℃ .It is called fusible coal and easy to slag and belongs to a typical kind of easily coking coal.The calculation results of slagging discrimination index show that 4 indexes are evaluated as " serious",1 index is evaluated as " medium",meaning high slagging tendency.In general,the change of coal type and the low melting temperature of the coal are the essential factors affecting the combustion coking of the boiler.To further solve practical problems,the acid-base equilibrium of coal ash was destroyed to increase the melting temperature and the particle size was refined by the following methods,5%quartz was blended into the coal to increase the content of Si O2 and thus increase the melting temperature of the coal to 1 280 ℃,and the temperature would be increased by 110 ℃ .The frequency of pulverized coal mill was turned up from 19 Hz to 22 Hz to increase the sieving rate of pulverized coal particle size( 200 mesh) from 70% to 85%.Eventually,the boiler ran smoothly and the coking condition is improved significantly.Overall,the combustion adjustment measures achieve good results and relevant experience are available for reference.