Research About Gas-solid Two-phase Flow Character For A350m W Down-fired Boiler

The proportion of the hard coal accounts in our country is a large number,achieved40%above, down-fired boiler has obvious advantages compared with theother type furnace, but for a long time in the past this kind of technology has beenforestalled. Through10years of unremitting efforts, after the digestion andabsorption of innovation, our country has put forward the theory of multi-injectionmulti-stage combustion.This topic research object for the power plant is a350MW down-fired boilerthat uses "multi-injection multi-stage combustion" technology. A gas-solid two-phase cold modeling test-bed is built, and the scale of boiler model is1:20, onwhich the measuring system of PDA is used to study the gas-solid two-phase flowcharacteristics. Results are as follows.When the secondary under-arch air rate reduced from25%to15%, thesecondary air rate on-arch is increasing. Thus the sub speed of the downwardairflow from furnace arch on the vertical direction is increasing, so as to theundershoot depth of two-phase downstream airflow. And the reduction of thesecondary under-arch air rate makes reduced the impediment of the secondaryunder-arch air to the on-arch two-phase downstream airflow, which ultimatelycaused serious erosion of cold ash bucket by the two-phase downstream airflow.Results of the contrast between the gas and solid phase show that when the arch-below air ratio is15%, the fluctuating velocities is much less than25%, indicatingthat arch-injected coal particles mixing well with a higher speed of arch-below airflow. Considering the erosion of cold dust hopper and the mixture of the gas-solidtwo phase, the optimum arch-below air ratio is25%.Experiments and analysis are taken for modeling boiler on the condition oflow load, which show that the sub speed attenuation of the downward airflow fromfurnace arch on the vertical direction is significantly decreased, and the undershootdepth is further increasing. Especially in the case of the back-wall burner outage,the two-phase gas flow from the front wall rushing to nearly the back-wall offurnace arch forms the U-shaped flow field obviously.According to the U-shaped flow field in the low load condition, atransformation program of normally through the secondary under-arch air at outageside is proposed, which can effectively alleviate the erosion of the hopper and theopposite combustion system by experiments.