## 3 Results and Discussion
### The Influence of Working Conditions on the Efficiency of Filter Media  
Based on the 50% PPS + 50% PTFE blended filter material commonly used in the power industry (sample 7), the filter efficiency of the filter material under different working conditions was investigated.  
2.1 Dust Filtration Efficiency of Filter Media under Different Constant Pressure Soot Cleaning Resistance  
According to the standard test conditions in Table 2. When the constant pressure soot cleaning resistance was 800 Pa, 1000 Pa, and 1500 Pa, respectively, the filtration efficiency of sample 7 was determined, and the results were shown in Figures 5 and 6.  
Figure 5: Filtration efficiency of filter media for total dust at different constant pressure soot cleaning resistances.  
Figure 6: PM\({}_{25}\) filtration efficiency of filter media at different constant pressure soot cleaning resistances.  
1. Compared with PI and PTFE, PPS filter media had the highest filtration efficiency and the best filtration performance stability after a long period of operation.
2. Increasing the mass per unit area of the filter media could improve the filtration performance, but the advantages will become less and less in the long term.
3. The filtration effect of coated filter media was not as good as impregnation treatment because of the influence of the film formation process.
4. Membrane-coated filter media showed the highest filtration efficiency, gradient filter media filtration performance was the second, followed by conventional filter media, ordinary blended, and blended ultrafine filter media.
5. Changes in the experimental conditions had different effects on the dynamic dust filtration performance of the filter media. The filtration efficiency of the filter media increased with the increase of the constant pressure cleaning resistance. The filtration efficiency was slightly affected by the change in the inlet dust concentration, but decreased with the increase in filtering velocity.  
The above test results and analysis provide a theoretical basis for the selection of filter media for engineering projects, especially for projects with ultra-low emission requirements, providing a range of options for high precision filtration media, such as membrane-coated filter media and gradient filter media. Unfortunately, due to the time factor and the limitations of the experimental conditions, the effect of different filter materials and experimental conditions on the dust removal performance was only studied at room temperature and a low concentration (inlet concentration of only 5 mg/m\({}^{3}\)). In fact, the actual working conditions of the filter media in the project are more complex, which has a certain influence on the use of the filter media, and its performance in actual engineering will be studied in depth in the next step.  
K.C.: conceptualization, writing--original draft preparation, data curation, methodology; Y.H.: writing--review and editing, funding acquisition, supervision, project administration; S.W.: validation, software; Z.Z.: data curation, investigation; H.C.: methodology. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the National Key R&D Program of China (2017 YFB0603203).  
The authors declare no conflict of interest.