| Under the policy background of ultra-low emission technology transformation in China,the mass concentration of particulate matter discharged by coal-fired power plants has been greatly reduced,which puts forward higher requirements for the monitoring system of the latter.The traditional measurement system using the filter membrane enrichment method requires a long sampling time to detect the mass concentration of particulate matter,and cannot realize online real-time measurement.Although the non-sampling light scattering measurement method has the advantages of real-time online measurement,when the concentration of particles is low,if there is no front enrichment device to accumulate the mass of particles,the error of the real-time measurement of the mass concentration of particles is large.In view of the physical characteristics of ultra-low emission particulate matter from coal-fired sources and the limitations of the existing measurement system for mass concentration of particulate matter,a particulate enrichment device based on injection and bubbling technology was proposed in this paper.It can integrate the mass accumulation of particles and the on-line real-time measurement of light scattering,and provides a new possibility for measuring the mass concentration of ultra-low emission particulate matter.Through numerical simulation and experimental analysis,the structure optimization design and operation mode selection are carried out in order to improve the enrichment efficiency of jet bubbling particulate enrichment device and reduce the escape of particulate matter,so as to improve the accuracy of later measurement.The specific research contents are as follows:1.According to the requirements of the particulate concentration measurement system,a preliminary physical model of the particulate concentration device was constructed based on the injection bubbling technology.Its profile size is 150mm in diameter and H/D=3.2.The aeration pipe(DN16mm)adopts the down-flow air inlet mode.The washing liquid in the enrichment device is distilled water,which is directly stored in the enrichment device without circulation.2.The operation characteristics of the preliminary enrichment device were analyzed on the numerical simulation platform,and the results showed that the enrichment efficiency of the preliminary designed enrichment device for large-particle size particles was higher under the condition of the gas-solid flow rate of 5m/s and the immersion depth of the aeration pipe of100mm.For particles of small size,the gas-liquid mixture in the enrichment device is not sufficient,which makes it easy to follow the gas overflow,and the enrichment efficiency is relatively low.For 10 micron particles,the enrichment efficiency was only 88.24%.In view of the low concentration efficiency of small particle size particles in the preliminary design of the enrichment device,this paper further proposes to improve the gas-liquid mixing characteristics of the enrichment device by reducing the size of the aeration pores and adding stirring device,so as to improve the concentration efficiency of small particles and realize the structural optimization of the enrichment device.The results show that when the size of aeration hole is 3mm,the proportion of small bubbles accounts for 53.47%,and the enrichment efficiency of 10-micron particles can be improved to 88.84%.When the impeller was close to the aeration pipe outlet,the dispersion effect of the gas phase in the enrichment device was the most obvious,and the enrichment efficiency of 10-micron particles was improved to 91.40%.Therefore,the optimal size of the aeration hole is 3mm(14 holes);The stirring paddle shall be installed above the non-coaxial air outlet of the aeration pipe and close to the air outlet.3.According to the optimized structure of the numerical simulation,the enrichment device of spray bubbling particles was processed,and the enrichment characteristics were studied experimentally.The results showed that the most important factor affecting the concentration efficiency of particulate matter was the immersion depth of aeration pipe,the second influencing factor was the stirring speed,and the third influencing factor was the inspiratory capacity.The optimal operation mode of the particle enrichment device is 3.2m~3/h of inspiratory capacity,125mm of immersion depth of aeration pipe and 450rpm of stirring speed.At this time,the total concentration efficiency of the corresponding particles reaches the maximum,which is 92.68%.According to the above results,under the optimal structure and operation mode of the enrichment device constructed in this paper,the total enrichment efficiency of the particulate matter reached the highest 92.68%,and there were still 7.32%of the particulate matter overflow enrichment device,which still needed to be improved in the later stage. |
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