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 10 μL/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.