QIN Jingyuan，ZHANG Yulu，JIANG Jialing，XU Menghao，CHEN Haiyan，LIN Longyuan

School of Environment and Resource， Southwest University of Science and Technology， Mianyang 621000， China

Abstract

Objective With the advancement of powder processing technology, polyvinyl chloride (PVC) powder has been widely used as a synthetic material in various fields such as plastic products, building materials, pipes, and cables. However, the electrostatic buildup risk during powder processing has gradually become apparent. During the production, transportation, processing, and storage of PVC powder, friction and collisions between particles, as well as between particles and pipelines, equipment, and containers, lead to the accumulation of electrostatic charge. When the accumulated charge reaches a certain level, electrostatic discharge can occur, potentially igniting the powder and causing fires or explosions, resulting in casualties and property damage to enterprises. The study aims to explore the impact of moisture content, feeding rate, and conveying speed on the electrostatic charge quantity in PVC powder during pneumatic conveying and to reduce the generation of electrostatic charge and the risk of electrostatic discharge.

Methods In this study, a self-built pneumatic conveying platform was used to conduct experimental research on PVC powder with different moisture contents under varying feeding and conveying speeds. First, 2 kg of PVC powder was taken, and the moisture content (d) was adjusted by changing the mass ratio of water to PVC powder. Five groups of samples with moisture contents of 0%, 1%, 2%, 3%, and 4% were prepared, labeled as S0, S1, S2, S3, and S4, respectively. After sample preparation, the effect of moisture content on the charge-to-mass ratio at different feeding rates was investigated. Based on the recommended conveying speed for PVC powder in pneumatic conveying， a conveying speed of 9. 1 m/s was selected. The 2 kg of PVC powder was then fed over durations ranging from 1 to 5 minutes. After the conveying experiments, samples were taken from the ash bunker and placed in a Faraday cup to measure the electrostatic charge. The mass of the samples was also measured, and the charge-to-mass ratio of the PVC samples was calculated. Based on the results of the previous experiments, an optimal feeding rate of 6. 7 g/s was selected as the fixed parameter for this set of experiments. The conveying speed was then adjusted by changing the speed of the induced draft fan, with five different conveying speeds of 7. 9, 9. 1, 10. 3, 11. 2, and 14. 8 m/s, to investigate the effect of moisture content on the charge-to-mass ratio at different conveying speeds.

Results and Discussion When the moisture content of the PVC powder was constant, the charge-to-mass ratio decreased with an increase in feeding rate and increased with an increase in conveying speed. When the feeding rate increased from 6. 7 g/s to 33. 3 g/s, the charge-to-mass ratio decreased the most for powder with 0% moisture content, from 14. 581 μC/kg to 7. 325 μC/kg. However, when the moisture content was 3%, the feeding rate had little effect on the charge-to-mass ratio. When the conveying speed increased from 7. 9 m/s to 14. 8 m/s, the charge-to-mass ratio increased the most for powder with 0% moisture content, from 5. 435 μC/kg to 34. 891 μC/kg. However, when the moisture content was 2%, the conveying speed had little effect on the charge-to-mass ratio. At the same feeding rate, the higher the moisture content of the PVC powder, the lower the charge-to-mass ratio. When the feeding rate was 6. 7 g/s, the charge-to-mass ratio changed the most with moisture content, decreasing from 14. 581 μC/kg to 0. 008 μC/kg as the moisture content increased from 0% to 4%. However, when the moisture content increased from 3% to 4%, the charge-to-mass ratio decreased by only 0. 029 μC/kg, indicating that further increases in moisture content beyond 3% had little effect on the charge-to-mass ratio. At the same conveying speed, the higher the moisture content of the PVC powder, the lower the charge-to-mass ratio. When the conveying speed was 14. 8 m/s, the charge-to-mass ratio changed the most with moisture content, decreasing from 34. 891 μC/kg to 0. 212 μC/kg as the moisture content increased from 0% to 2%. However, when the moisture content increased to 3%, the conveying pipeline became blocked during the pneumatic conveying experiments. Based on the charge-to-mass ratio at different conveying speeds for PVC powder with 2% moisture content, it was found that a moisture content of 2% was sufficient to meet engineering application requirements.