【作者】 赵勇纲；

【导师】 孙保民；

【作者基本信息】 华北电力大学 ， 热能工程， 2014， 博士

【摘要】 煤粉锅炉是我国燃煤机组的主力设备。燃烧优化是提高煤粉锅炉性能的有效途径。燃烧系统测量的准确可靠是实现燃烧优化的基础。由于设备的限制,燃烧系统的测量条件比较恶劣,烟、风和煤粉管道可供测量的直管段很短,因此,研究短管道中气相及气固两相流体平均流速测量方法,并开发适用于煤粉锅炉燃烧系统的管道气体和气固两相流体高精度、低阻力平均流速在线测量装置具有重要的意义。本文详细分析了目前在锅炉燃烧调整中经常使用的一些测量装置的结构、功能、使用范围及其优缺点,根据煤粉锅炉燃烧系统管路的结构特点,提出了实现锅炉燃烧系统喷口平均风速准确测量的必要条件。通过对现有的各种形式、测量原理的流量测量装置的分析比较,提出了基于伯努利流体动压测量原理和附面层理论,采用格栅整流、感压孔管道全截面分布、多排孔取压、单元测量、大腔体均压、共同引压,流线型机翼优化技术降低阻力等测量实现方法。从数学上证明了可以利用平均压力进行流量计算,分析了引压的阻力条件及其对格栅数量的要求,采用数值计算的方法验证了格栅整流的效果和本文提出的测量方法的可靠性,确认了该方法中测点安装误差对测量结果影响很小,具有良好的应用前景。进而利用一次元件增大动静压差,开发了气体、气固两相流体管道平均气体流速测量装置。根据模化原理及相似条件设计搭建了冷态实验系统,在实验台上对本文提出的风速测量装置进行了相关性能的实验研究。通过冷态实验,确定了输出压差信号大、阻力小的直线型机翼(扩散角α=11°)。冷态实验研究表明,包括整流格栅在内的双、四翼体测量装置局部阻力系数的数值很小,为0.08-0.13。随着流通截面比m的减小,测量装置的输出压差信号增大。当Re>1×104时,测量装置的流量系数基本趋于一致,与Re数无关。m=0.4、0.5时,输出信号更为稳定,测量误差较小。加装整流装置与没有加装整流装置相比,测量信号稳定性好,测量误差较小。感压孔的数量和在测量管道截面上的不同划分方法对于短管道条件下不均匀流场的准确测量影响较大。通过加装整流装置,合理布置测量元件和感压孔的数量及位置,在直管段很短,甚至没有的条件下,测量装置的测量误差小于2%。气固两相的实验结果表明,本文开发的流量测量装置的局部阻力系数很小,对于流通截面比m在0.04-0.18范围内,局部阻力系数ξ在0.1-0.3之间。当Re大于1×105时,测量装置的流量系数趋于一致,不随Re数变化。当测量装置上游有2倍、下游有0.5倍当量直径长度的直管段时,可以保证测量误差小于2%。由于安装不当或气流偏斜造成角度不当,只要角度小于6°,引起的误差小于1%。两相流体浓度的变化对测量装置流量系数的影响非常小,现场应用可以忽略不计。工业应用实践表明,本文提出的测量系统可以实现锅炉燃烧系统喷口风速的实时准确测量,风速测量的误差小于3%。由于可以精确测量燃烧器喷口风速,为锅炉燃烧优化提供必要条件,可以提高锅炉热效率1%～2%,降低NOx排放30%左右。更多还原

【Abstract】 Pulverized coal (PC) fired boiler is the main unit for electric power generation in China. Combustion optimization is very important to improve the performance of PC boiler, which depends strongly on the measurement accuracy and reliability of combustion system. However, the flow rate measurement of combustion system is very difficult due to the limitation of the combustion equipment. The straight pipe is normally short for measuring flow rate in the air duct. This requires a real-time and accurate measurement method of the average flow rate of gas as well as a gas-solid two-phase flow in a pipeline with a lower pressure drop.The up-to-date structure, function and principle of the update flow meters used in the combustion system in PC boiler were investigated in this thesis. On accordance with the structure of the pipeline in the combustion system in PC boiler, the necessary condition to real-time and accurately measure the flow rate was suggested. Based on the comparison and analysis of these meters with different structures and principles, a novel average flow meter was suggested in gas flow or gas-solid two-phase flow. Its principle is local different pressure of fractional unit with parallel wings with distributed pressure measurement holes for gas flow or parallel back pipes with different lengths, where the three dimensions flow caused by the short straight pipe was straighten out by screen grid, and the local pressure are introduced to a common vessel. The average pressure was suggested to predict the flow rate, which is reasonable mathematically. The pressure resistant condition for the average pressure measuring as well as the screen grid size was deduced. The flow rectification and the reliability of the suggested flow meter were confirmed by the numerical simulations. And it was found that it is very insensitivity for installation deviation for the measurement, which indicates it could be used in the industrials. With the enlarged the different pressure by the primary unit, the flow meter was developed for gas and gas-solid two-phase flow. In the meter, the screen grid is distributed fully in the meter section. To further understanding the performance of the meter and improve continuously its structure, a cold test facility was designed and set up based on the scaling law and similarity conditions. And the experimental investigations were conducted.According to the cold test, it was found that the straight line wing is better with larger different pressure and lower pressure drop. And straight line wing with expanding angle of11°was selected for the meter. The experimental results showed that the pressure coefficient of the gas flow meter including the screen grid and the wings is very low ranging from0.08to0.13. With the decreasing of sectional area ratio m, the output of different pressure increases. The flow rate coefficient of the meter tends to a constant independent from Reynolds number when Reynolds number is higher than1×104. When the sectional area ratio m=0.4and0.5, the measurement error is extraordinary lower with more stable different pressure. The screen grid for rectification stabilizes the different pressure output with lower measurement error compared that without screen grid. The pressure measuring holes number and its distribution affects the measurement results. When the straight pipe is very short even0, the measurement error is less than2%with screen grid and reasonable wing with pressure measuring holes number and its distribution.The experimental results of gas-solid two-phase flow showed that the pressure coefficient of the gas flow meter of gas-solid two-phase flow is also very low ranging from0.1to0.3when sectional area ratio m decreases from0.18to0.04. The flow rate coefficient of the meter tends to a constant independent from Reynolds number when Reynolds number is higher than1×105. When the sectional area ratio m=0.4and0.5, the measurement error is extraordinary lower with more stable different pressure. When the straight pipe is2.5times diameter, the measurement error is less than2%. The additional error is less than1%caused by the angle less than6°departure. And the effect of the solid density in the gas-solid two-phase flow on the measurement can be ignored because it is very small.The flow meter suggested in this thesis was applied in the boilers for real-time measuring. The practices proved its accuracy and reliability with error of less than3%. The flow meter provides a reliable equipment for automatic optimization of combustion, leading to the boiler thermal efficiency increases1%with30%NOx reduction.更多还原