| The pollutants generated by fuel combustion,such as particulate matter(PM),NOx,SO2,etc.,have been widely concerned by scholars.Through research,it has been found that there is still a type of particulate matter that has not been included in the emission list-condensable particulate matter(CPM),which is affecting the environment and threatening human health.The CPM measurement method has always been a widely studied direction.In response to the gap in CPM measurement methods,this paper proposes a new method based on dilution cooling method to connect particulate matter online monitoring equipment to achieve CPM online measurement.This article first optimized the structure of the dilution cooling sampling system,using Ansys Fluent simulation to determine the size of the dilution cooling chamber.Finally,it was determined that the dilution ratio of the dilution cooling sampling system was 5～20,the residence time was 10～34 seconds,the diameter of the dilution chamber was 20 cm,and the length was 125cm.A new dilution cooling sampling system has been developed.The innovation of this system is mainly reflected in the flow mode of mixed gases,the mixing mode of flue gas and air,and the regulation of the wall temperature of the dilution chamber.The dilution gas purification performance,airtightness,mixing uniformity,and particulate matter loss of the system were evaluated,and the results showed that the dilution cooling sampling system met the performance requirements.The dilution cooling sampling system and the laboratory one-dimensional settling furnace were used to optimize the system parameters through experiments at different dilution ratios and wall temperatures of the dilution chamber.The experimental results showed that the dilution ratio had little effect on the CPM measurement results within the range of 5～20.And as the wall temperature increases from 30℃ to 180℃,the CPM measurement results show a trend of first increasing and then decreasing,reaching the highest value at 80℃.The reason why the data increases first and then decreases is related to the thermophoretic effect between the gas and the wall,as well as the temperature of the mixed gas.Comparative experiments were conducted on the impinger cooling method and dilution cooling method at different sampling temperatures.The experimental results showed that the CPM measurement results using dilution cooling method were significantly smaller than those using EPA Method 202 for CPM collection.This is due to the following reasons:EPA Method 202 requires tedious steps before weighing CPM,which can easily introduce operational errors;EPA Method 202 can cause the dissolution of soluble gases such as SO2,resulting in higher CPM measurement results;When using the dilution cooling method for experiments,CPM will condense on the walls and connecting pipelines,causing significant losses that cannot be ignored.In addition,the measurement results of the two methods show an increasing trend in CPM measurement data as the sampling temperature increases.This is because as the flue gas temperature decreases,certain substances in CPM reach their phase transition points,and before reaching the CPM sampling device,they transition from a gaseous state to a solid/liquid particle state,resulting in a decrease in CPM in the flue gas as the flue gas temperature decreases.The dilution cooling sampling system was used to connect β X-ray absorption dust detector and electrical low pressure impactor(ELPI)to achieve online measurement of CPM concentration and particle size at different sampling temperatures and dilution ratios.The results showed that the measurement data obtained by the two online monitoring devices were consistent with the data obtained by the dilution cooling method and the filter membrane weighing method,indicating that the online measurement method designed in this project can obtain real-time CPM concentration and particle size data.The experimental data patterns presented in this article have important reference value in future CPM research,and the measurement methods proposed in this article provide new ideas for the development of online CPM measurement methods. |
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