基于TDLAS和恒流稀释取样的磨煤机出口痕量CO体积分数在线监测技术研究

On line monitoring technology of trace CO volume fraction at the outlet of coal mill based on TDLAS and constant-flow dilution sampling

磨煤机运行参数直接影响着燃煤机组的运行安全和燃烧性能,实时在线监测磨煤机出口CO体积分数并基于监测数据进行安全预警具有重要意义。首先基于可调谐二极管激光吸收光谱(TDLAS)和赫里奥特(Herriott)多次反射池开展波长调制-直接吸收光谱(WM-DAS)法测量精度及检测限验证实验。实验结果表明,在1~10μL/L内CO测量值与配气值一致且检测限可低至5.2×10^(-3)μL/L(300 s),具有极高的灵敏度和测量精度。随后基于原理实验研制痕量CO体积分数在线测量系统,并结合烟气恒流稀释高保真预处理技术,将研制的痕量CO体积分数在线监测系统应用于火电机组磨煤机现场,采用多点轮测方式实现了单台火电机组5台磨煤机出口CO在线监测及安全预警。最后结合磨煤机出口温度等监测数据对一次风温进行调整,可在确保磨煤机安全运行基础上提高锅炉效率。

The operating parameters of coal mills directly affect the safety and combustion performance of coalfired units.Therefore,it is of great significance to carry out real-time monitoring of CO volume fraction at the outlet of coal mills and accordingly have safety early warning based on the monitored data.In this work,the measurement accuracy and detection limit of wavelength modulation direct absorption spectroscopy(WM-DAS)method were verified based on tunable diode laser absorption spectroscopy(TDLAS)and Herriott multi-pass cell.The experimental results showed that the measured CO volume fraction agree very well with the preset values in the range of 1 to 10μL/L,and the detection limit can be as low as 5.2×10^(-3)μL/L(300 s),which suggests the extremely high measurement sensitivity and accuracy of this method.Subsequently,based on this prototype experiment,an on-line monitoring system for the trace CO volume fraction was developed.Then,combined with the high-fidelity pretreatment technology of fuel gas based on the principle of constant-flow dilution,an on-line monitoring system for trace CO volume fraction was developed and applied to the outlet of coal mill of thermal power unit.The online CO monitoring and safety warning at the outlet of 5 coal mills of a single thermal power unit were realized by using multi-point alternating measurement strategy.With the monitored CO volume fraction and temperature of the coal mill outlet,the temperature of the primary air is adjusted to improve the boiler efficiency while ensuring safe operation of coal mill.