生物质燃料是替代化石燃料的重要能源,在燃煤机组上掺烧生物质是当下生物质能利用的主要途径。由于煤和生物质耦合燃烧过程中存在协同效应,生物质燃料与煤耦合燃烧性能与二者单独燃烧的燃烧性能差异无法通过化学成分或相关性质算术平均来确定,与此同时,生物质中富含的碱金属K也会加重受热面结渣倾向。为研究煤与生物质混合燃烧过程中协同效应,选取神府烟煤与板栗壳作为试验样品,通过混合、研磨与压制,制备成圆饼形颗粒并在Hencken平焰燃烧器上进行燃烧试验。利用高速摄像机结合图像处理技术计算着火延迟时间,利用光谱仪结合自发辐射理论测量燃烧过程中火焰温度、气相K浓度。探讨耦合燃烧着火特性、燃烧特性与气相碱金属释放特性协同效应及其原因。最后,结合灰分分析结果计算各工况结渣指数,获得燃烧气相碱金属释放量与结渣指数相关性关系。结果表明:煤与生物质耦合燃烧着火延迟时间低于理论值,证明耦合燃烧着火存在协同效应,表现为促进着火。受纤维素热解与碱金属元素催化共同影响,生物质质量分数为50%时,着火延迟时间与理论值之差达到最大1.91s,协同效应最大;耦合燃烧释放的碱金属低于理论值,说明耦合燃烧气相碱金属释放协同效应表现为抑制气相碱金属释放,由挥发分-焦炭相互作用与无机反应共同控制,无机反应中Si、Al元素与K反应占主导;随气相K释放量增大,碱酸比与硅比数值增大,结渣倾向升高,结渣指数与气相K释放量间相关性系数均大于95%,说明气相K释放量与结渣指数高度相关,可见在线监测获得的气相K释放浓度具有判别结渣特性潜力。

Biomass fuel is a promising alternative of fossil fuels. Co-combustion biomass in coal-fired power plants is currently a primarymethod of utilizing biomass energy. Due to the synergistic effect in the coupled combustion process of coal and biomass, the difference between the combustion characteristics of co-combustion of biomass with coal and those of two alone cannot be determined through the arithmetic average of chemical composition or related properties. The high potassium content in biomass exacerbates the slagging tendency onthe heating surface. To investigate the synergistic effects during the co-combustion of coal and biomass, Shenfu bituminous coal and chestnut shell were selected as experimental samples. These materials were prepared into shaped pellets by mixing, grinding, and pressing forcombustion experiments conducted on a Hencken flat-flame burner. The ignition delay time was determined via using high-speed camerascombined with image processing technology. The flame temperature and gaseous K concentration during the combustion process were measured using a spectrometer based on flame emission spectrum theory. Then, the synergistic effects and reasons of ignition, combustion, andgaseous alkali metal release characteristics during co-combustion were investigated. Finally, the slagging index for various conditions wasobtained using the results of ash analysis and the correlation between the release of gas-phase alkali metals and the slagging index was established. The results show that the ignition delay time under the co-combustion condition is lower than the theoretical value, confirmingthe existence of synergistic effects during ignition, which is characterized by the promotion of the ignition through the influence of cellulosepyrolysis and alkali metal catalysis. The difference between ignition delay time and theoretical value reaches the maximum value of 1.91 sunder 50% biomass mass fraction, indicating the maximum synergistic effect. The release of gaseous alkali metals during co-combustion islower than the theoretical value, indicating that the synergistic effect in gaseous alkali metal release during co-combustion acts as an inhibitory factor. This inhibition effect is attributed to the volatile-coke interaction and the inorganic reactions in which the reactions of Si,Al with K dominates the synergistic effect. As the release of gaseous K increases, the values of base-acid ratio and silica ratio increase,the tendency of slagging also increases. The correlation coefficients between the slagging indices and the release of gaseous K are both morethan 95%, indicating that the release amount of gaseous K is highly correlated with the slagging index. It can be seen that the release ofgaseous K obtained by online monitoring has the potential to predict the slagging tendency.

0 引言

1 试验

   1.1 试验样品准备

   1.2 试验仪器与工况

2 测量原理

   2.1 着火延迟时间定义

   2.2 火焰温度、气相K浓度与热辐射计算

   2.3 结渣指数计算

3 试验结果与分析

   3.1 着火特性

   3.2 火焰温度与气相K释放特性

   3.3 结渣特性

4 结论