Design And Optimization Of High-precision Sampling Experimental Device For As、Se And Pb Under Flue Gas Conditions

With the development of science and technology and the improvement of people’s awareness of environmental protection,trace heavy metal elements with low content of coal and small total emissions have gradually attracted people’s attention.Therefore,how to reduce the emissions of trace heavy metals has become the focus of research.To achieve high-precision sampling of three heavy metals,arsenic,selenium,and lead,this article improves and innovates on the basis of EPA-method29,and builds a set of small-scale laboratory thermal smoke simulation device and smoke sampling device.The hot flue gas simulation device includes a micro-feed system,a gas distribution system,a gas preheating system,a fly ash heating system,a soot main settling furnace system,and a post-processing system.The sampling port is arranged at the bottom of the sedimentation furnace,and the flue gas sampling device connected to the sampling tube extends into the sampling port for sampling.Experimental research.After debugging the overall device,the influence of different flue gas temperatures on the sampling accuracy was first studied.In order to achieve sampling accuracy that can simulate a wide temperature range,the flue temperature was set to 40-600°C.EPA-method29 stipulates that the preheating temperature of the sampling tube is always maintained at 120°C±14°C.In this study,it was found that the preheating temperature of the sampling tube was consistent with the simulated flue temperature during the experiment.Compared with EPA-method29,the heavy metal recovery rate Major changes have taken place.If the temperature of the sampling tube is maintained at 120°C,the recovery rate will be reduced when the actual flue gas temperature is higher than 120°C.After using the improved method,the recovery rates of the three heavy metals of As,Se,and Pb will be increased to 80%,75%,85%or higher.At the same time,the effect of different flue gas conditions on the recovery rate was studied,and experiments have shown that when SO₂ is present in the flue gas,the mass recovery of Pb will be improved,and the standard deviation of the mass recovery rate will be reduced.However,the presence of NO has no significant effect on the mass recovery of the three heavy metals.Numerical simulation.In order to further explore whether the fly ash particles and simulated flue gas can be mixed uniformly under the set conditions in the main settling furnace to achieve constant velocity sampling,the numerical simulation of the main settling furnace is studied.Due to the low temperature of flue gas,the possibility of chemical reaction between fly ash and simulated flue gas is small.In order to simplify the model,the chemical reaction and phase change between fly ash and simulated flue gas are not considered;Ash deposits on pear-shaped glass containers,quartz tube walls and sampling tubes.By analyzing the pressures distributions contour,pelocity distributions contour and particle trajectory in the simulation,it can be preliminarily determined that the fly ash can be mixed with the flue gas evenly before the sampling port under the set conditions.